Apparatus and method for producing single crystal

ABSTRACT

An apparatus having a crucible ( 1 ) for holding a raw material, a heating means ( 11 ) for heating the raw material in the crucible ( 1 ) and a crystal transporting means ( 17 ) for transporting a seed crystal ( 13 ) upwards from the inside of the crucible ( 1 ), which further comprises a heat conducting member ( 3 ) which extends upwards at least from the vicinity of the upper end of the crucible ( 1 ), surrounds a single crystal ( 15 ) formed, and is made of a material having heat conductivity, and an interface portion radiation heat blocking member ( 7 ) for blocking, at least during cooling after the formation of a single crystal, the radiation heat toward an upper portion above the interface between a taper portion ( 15   a ) of the formed single crystal ( 15 ) connecting with the seed crystal ( 13 ) and a straight bulge portion ( 15   b ) having a cylindrical shape connecting with the taper portion ( 15   a ) of the formed single crystal ( 15 ). The use of the apparatus reduces the temperature difference in the radius direction of the single crystal ( 15 ), resulting in the reduction of the occurrence of defects or cracks, which leads to the reduction of the fraction defective in production of single crystals.

This application is a 371 of PCT/JP03/07493 Jun. 12, 2003

TECHNICAL FIELD

The present invention relates to a technology of producing a singlecrystal used for electronic equipments, medical apparatuses, and thelike.

BACKGROUND ART

In a known technology of producing a single crystal, a seed crystal isbrought into contact with a melt of a heated raw material, and this seedcrystal is pulled up, so that a single crystal is produced. In general,the formation of the single crystal is performed by the followingprocedure. A crucible holding a raw material of a single crystal andprovided with a surrounding heating device is disposed in the inside ofa furnace, the crucible is heated by the above-described heating device,and a melt of the raw material is heated by the crucible heated to ahigh temperature. When a seed crystal having a diameter smaller than thediameter of the single crystal to be produced is brought into contactwith the surface of this melt, the melt brought into contact with theseed crystal dissipates heat through the seed crystal and is cooled, sothat a crystal grows while being aligned in the direction of the crystalof the seed crystal. The seed crystal is pulled up in accordance withthe growth of the crystal, the grown crystal is cooled sequentially and,therefore, the crystal further grows. This is repeated, and the singlecrystal is produced. In the initial stage of growth of the singlecrystal, in order to increase the diameter of the crystal, a taperportion having a diameter becoming conically increased from the seedcrystal is formed while the seed crystal is pulled up. When the diameterof the seed crystal reaches a predetermined size, the formation of thetaper portion having a diameter becoming gradually increased isterminated, and the formation of the straight body portion is started,wherein the crystal grows cylindrically in the axis direction.

At this time, since the liquid level of the melt is positioned below theupper end of the crucible, the single crystal being pulled up is heatedby application of the radiation heat from the inner perimeter of thecrucible while the crystal is positioned below the upper end of thecrucible, and a portion of the single crystal positioned higher than theupper end of the crucible dissipates heat and is cooled. After anadequate length of straight body portion is formed, the straight bodyportion is isolated from the melt, and the amount of heating of thecrucible is reduced gradually and the crucible is cooled to roomtemperature.

In such a technology of producing a single crystal, when defects,cracks, and the like occur, portions including the defects, cracks, andthe like become defective portions, so that no product is available.Therefore, it is necessary for an improvement of the productivity toreduce the occurrence rate of defective portions, i.e. the fractiondefective. One of the causes of occurrence of defects, cracks, and thelike in the single crystal is attributed to a temperature distributionin the single crystal during the formation of the single crystal andduring the cooling of the formed single crystal.

With respect to a technology of producing a single crystal toappropriately adjust such a temperature distribution, i.e. temperaturegradient, in the single crystal in a longitudinal direction during theformation of the single crystal and during the cooling of the singlecrystal, Japanese Unexamined Patent Application Publication No. 8-175896proposes that a radiation heat reflector is disposed above a singlecrystal so as to suppress the heat dissipation toward an upper portionabove the single crystal, and the radiation heat reflector is movedupward as the single crystal is pulled up. Japanese Unexamined PatentApplication Publication No. 6-157187 proposes that a movable refractorylid is disposed on the upper opening of a furnace containing a cruciblefor producing a single crystal. In addition, Japanese Unexamined PatentApplication Publication No. 2001-316195 proposes that a lid is disposedon the upper portion of a crucible for producing a single crystal.

On the other hand, natural convection caused by a density gradientresulting from a temperature gradient of a melt in a crucible, Marangoniconvection caused by a surface tension gradient, and the like occur inthe melt in the crucible. When these types of convection of the meltoccur, a portion at which the single crystal is formed, i.e. asolid-liquid interface portion of the single crystal, does not becomeflat, but becomes concave or convex, for example. Consequently, atemperature distribution in the radius direction in the vicinity of thesolid-liquid interface portion of the single crystal becomes nonuniform.With respect to a technology of producing a single crystal to reducesuch nonuniformity of the temperature distribution in the vicinity ofthe solid-liquid interface portion of the single crystal, JapaneseUnexamined Patent Application Publication No. 6-183877 proposes thatwhen a single crystal is pulled up, the single crystal is rotated or acylindrical crucible is rotated in a rotational axis which is a centralaxis of a cylindrical crucible, forced convection to spread the melt inthe radius direction of the crucible is effected and, thereby, aconvection pattern of the entire melt is controlled in order to flattenthe shape of the solid-liquid interface portion of the single crystal.

In Japanese Unexamined Patent Application Publication No. 8-175896, atemperature distribution in the single crystal in a longitudinaldirection is reduced in the process of forming the single crystal inorder to reduce the occurrence of defects, cracks, and the like.However, when a radiation heat reflector is disposed at the positionimmediately above the single crystal, the difference in the temperaturedistribution in the single crystal in the radius direction duringcooling is increased and, therefore, it is difficult to reduce theoccurrence of defects, cracks, and the like. In Japanese UnexaminedPatent Application Publication No. 6-157187, the lid is disposed on theupper portion of refractory in a cooling process in order to reduce thecooling rate and to reduce the temperature distribution in the singlecrystal and, thereby, to reduce the occurrence of defects, cracks, andthe like. However, the control of the surface temperature of the singlecrystal in the process of forming the single crystal is not taken intoconsideration, so that the temperature distribution cannot be madeappropriate in the process of forming the single crystal, and it isdifficult to reduce the occurrence of defects, cracks, and the like aswell.

In Japanese Unexamined Patent Application Publication No. 2001-316195,since the lid is disposed on the upper portion of the crucible, thesurface temperature of the single crystal in an upper portion above thecrucible cannot be controlled in the cooling process, the temperaturedistribution cannot be made appropriate in the process of forming thesingle crystal as well, and it is difficult to reduce the occurrence ofdefects and cracks. In addition, since the lid is disposed on the upperportion of the crucible in the initial stage of the process of formingthe single crystal as well, the temperature of the surface of the taperportion of the single crystal, i.e. the taper surface, is raised, thesurface is roughened and, contrary to expectations, defects, cracks, andthe like may tend to occur. Consequently, these technologies ofproducing a single crystal may not reduce the occurrence of defects,cracks, and the like, and it is difficult to reduce the fractiondefective.

On the other hand, in high-frequency induction heating by the use of ahigh-frequency generation device including a high-frequency coil as aheating device, the heating value per unit volume in a unit time isproportional to the square of the current J_(θ) in the circumferentialdirection, the current being induced on the surface of the metal. TheJ_(θ) increases as the metal is located closer to the coil. Theelectromagnetic field has a property of concentrating on the surface ofthe corner portion of the metal. Therefore, when the cylindricalcrucible is heated by the high-frequency induction heating, theelectromagnetic field concentrates on the upper end portion of the sidewall of the crucible and the periphery of the bottom serving as thelower end portion. Consequently, the heating values at the upper endportion and the lower end portion of the side wall of the cruciblebecome larger than those of other portions. In this manner, for example,as the side wall becomes longer in the axis direction than the diameterof the bottom, the temperatures of the portions of the side wall otherthan the upper end portion and the lower end portion of the side wall ofthe crucible become lower than the temperatures of the upper end portionand the lower end portion. Therefore, the temperature distribution ofthe crucible becomes nonuniform, and the melt exhibits an undesirableconvection pattern even when the seed crystal and/or the crucible arerotated as disclosed in Japanese Unexamined Patent ApplicationPublication No. 6-183877, so that the solid-liquid interface portion ofthe single crystal may not be flattened.

Furthermore, even when the solid-liquid interface portion of the singlecrystal can be flattened by effecting the forced convection to spread inthe radius direction through the rotation of the single crystal and/orthe crucible, as disclosed in Japanese Unexamined Patent ApplicationPublication No. 6-183877, in the process of forming the taper portionfrom the seed crystal, since the outer diameter of the crystal is smallcompared with that in the formation of the straight body portion of thesingle crystal, the forced convection to spread in the radius directioncannot be effected adequately. Consequently, in the stage of formationof the taper portion from the seed crystal, the melt in the crucible mayexhibits an undesirable convection pattern, so that the solid-liquidinterface portion of the single crystal may not be flattened, dependingon the conditions of the size of the bottom of the crucible and thelike. As described above, even in the technology of producing a singlecrystal disclosed in Japanese Unexamined Patent Application PublicationNo. 6-183877, since the solid-liquid interface portion of the singlecrystal is not flattened and the temperature distribution becomesnonuniform depending on the conditions of the size and the shape of thecrucible and the like, the occurrence of defects, cracks, and the likemay not be reduced, and it is difficult to reduce the fractiondefective.

DISCLOSURE OF INVENTION

The object of the present invention is to reduce the fraction defectivein the production of a single crystal.

One of primarily causes of the occurrence of defects, cracks, and thelike generated in a crystal is attributed to that the outer perimeterportion of the single crystal is cooled prior to the central portion ina cooling process and, thereby, the temperature distribution in thesingle crystal becomes nonuniform. In particular, the inventors of thepresent invention found out that the effect of the thermal stress due tothe temperature difference in the radius direction of the single crystalwas large whereas the thermal stress due to the linear temperaturedistribution in the longitudinal direction of the single crystal wassmall. In this manner, the inventors of the present invention found outthat it was effective to reduce the temperature difference in the radiusdirection of the single crystal by heating the outer perimeter of thecrystal in the cooling process. Also, in addition to the reduction ofthe temperature difference in the radius direction of the singlecrystal, it was effective to cool only the upper end surface of thesingle crystal, i.e. the taper surface of the taper portion, so as tomaintain the cooling rate by linearizing the temperature distribution inthe longitudinal direction.

Accordingly, an apparatus for producing a single crystal of the presentinvention is configured to comprise a crucible for holding a rawmaterial, a heating device for heating the raw material in the crucible,and a crystal transporting device for transporting a seed crystalupwards from the inside of the crucible, wherein the apparatus forproducing a single crystal further comprises a heat conducting memberwhich extends upwards at least from the vicinity of the upper endportion of the side wall of the crucible, which surrounds a formedsingle crystal, and which is made of a material having heat conductivityand, thereby, the above-described problems are solved.

By adopting such a configuration, when the single crystal leaving thecrucible is cooled, the heat of the crucible below the single crystal isconducted by the heat conducting member to an upper portion outside thecrucible, and the amount of the heat dissipated from the outer perimetersurface of the single crystal is reduced. In this manner, thetemperature difference in the radius direction of the single crystal isreduced. Consequently, the occurrence of defects, cracks, and the likecan be reduced, and the fraction defective can be reduced.

An apparatus for producing a single crystal of the present invention isconfigured to comprise a radiation heat blocking member of an interfaceportion between a taper portion, which is connected with the seedcrystal of the formed single crystal and has a diameter graduallybecoming increased, and a cylindrical straight body portion, which isconnected with the taper portion of the formed single crystal, of theformed single crystal for blocking the radiation heat toward an upperportion above the interface portion, at least during cooling after theformation of a single crystal and, thereby, the above-described problemsare solved.

In this manner, when the straight body portion of the single crystalleaving the crucible is cooled, the heat dissipation due to the radiantheat transfer from the outer perimeter surface of the straight bodyportion of the single crystal toward an upper portion is blocked and, inaddition, the flow of a relatively-low-temperature gas from an upperportion above the apparatus into the surroundings of the outer perimetersurface of the straight body portion of the single crystal is blocked.And, the temperature difference in the radius direction of the singlecrystal is reduced. Furthermore, only the taper surface of the taperportion of the single crystal can be cooled so as to maintain thecooling rate by linearizing the temperature distribution in thelongitudinal direction. Therefore, the occurrence of defects, cracks,and the like can be reduced, and the fraction defective can be reduced.

In addition, the radiation heat blocking member for blocking theradiation heat from the interface portion between the taper portion andthe straight body portion toward an upper portion can be transported ina vertical direction and, a radiation heat blocking member transportingdevice for transporting this radiation heat blocking member in thevertical direction is comprised. By adopting such a configuration, theradiation heat blocking member can be positioned at the interfaceportion between the taper portion and the straight body portion duringthe formation of the single crystal as well, and the radiation heat andthe like from the interface portion between the taper portion and thestraight body portion toward an upper portion can be blocked.Consequently, the occurrence of defects, cracks, and the like can befurther reduced, and the fraction defective can be further reduced.

The inventors of the present invention found out that another cause ofthe occurrence of defects, cracks, and the like generated in the crystalwas attributed to the occurrence of roughening of the surface resultingfrom an excessive rise in the temperature of the taper surface of thetaper portion during the formation of the single crystal. It iseffective for suppressing the roughening of the taper surface tosuppress the temperature rise of the taper surface of the taper portionduring the formation of the taper portion in the initial stage of thegrowth of the single crystal, while the taper portion of the singlecrystal is positioned in the inside of the crucible. On the other hand,during the formation of the straight body portion of the single crystalafter the taper portion of the single crystal is formed, it is effectivefor reducing the nonuniformity of the temperature distribution, i.e. thetemperature difference, in the radius direction of the single crystal inthe course of formation at the position of the liquid level of the melt,i.e. at the position of the solid-liquid interface, to increase the heatdissipation from the taper portion outside the crucible and to reducethe heat dissipation from the outer perimeter surface of the straightbody portion inside the crucible.

Accordingly, a method for producing a single crystal of the presentinvention comprising the step of heating a crucible holding a rawmaterial and pulling up a seed crystal while the seed crystal is incontact with a melt of the raw material so as to produce a singlecrystal, wherein the diameter of the single crystal is increased duringformation of a taper portion of the single crystal in an initial stageof growth of the single crystal, and the single crystal is cylindricallygrown connecting with the taper portion during formation of a straightbody portion of the single crystal, while the radiation heat whichreaches the taper portion of the single crystal from an inner surface ofthe crucible is blocked during the formation of the taper portion of thesingle crystal and, thereby, the above-described problems are solved.

An apparatus for producing a single crystal of the present invention isconfigured to comprise an in-crucible radiation heat blocking memberwhich surrounds a single crystal and which blocks the radiation heatfrom an inner surface of the crucible toward the single crystalpositioned in the inside of the crucible and an in-crucible radiationheat blocking member transporting device for transporting this radiationheat blocking member in a vertical direction, while the in-crucibleradiation heat blocking member transporting device transports thein-crucible radiation heat blocking member to the position surrounding ataper portion of the single crystal during formation of the taperportion of the single crystal to increase the diameter of the singlecrystal in an initial stage of growth of the single crystal andtransports the in-crucible radiation heat blocking member to theposition at a distance from the single crystal during formation of astraight body portion of the single crystal cylindrically grownconnecting with the taper portion and, thereby, the above-describedproblems are solved.

By adopting such a configuration, during the formation of the taperportion of the single crystal, the heating of the taper surface of thetaper portion due to the radiation heat from the inner surface of thecrucible is suppressed by the in-crucible radiation heat blockingmember, the temperature rise of the taper surface can be suppressed, andthe surface roughening of the taper surface can be suppressed. On theother hand, during the formation of the straight body portion of thesingle crystal, since the in-crucible radiation heat blocking member istransported to the position at a distance from the crystal, the heatdissipation from the taper portion of the single crystal toward an upperportion is not hindered, the outer perimeter surface of the straightbody portion of the single crystal positioned in the inside of thecrucible is applied with the radiation heat from the inner surface ofthe crucible and, thereby, a temperature drop of the outer perimeterportion of the straight body portion of the single crystal is reduced,so that the temperature difference in the radius direction of the singlecrystal at the surface of the crystal growth, i.e. at the position ofthe liquid level of the melt, can be reduced. Consequently, theoccurrence of defects, cracks, and the like can be reduced, and thefraction defective can be reduced.

Furthermore, in a desirable configuration, a heating device is ahigh-frequency generation device including a high-frequency coil whichis wound around the crucible while the axis is set in a verticaldirection and which is energized by a high-frequency current, and thein-crucible radiation heat blocking member surrounding the singlecrystal, for blocking the radiation heat from the inner surface of thecrucible toward the single crystal positioned in the inside of thecrucible, is made of a nonmetallic material, and is in the shape of acone provided with an opening capable of passing through the seedcrystal and a rod-shaped or band-shaped seed holder of a crystaltransporting device at the center or in the shape of a cylinder havingan inner diameter larger than the diameter of the straight body portionof the single crystal.

In a method for producing a single crystal of the present invention, thediameter of the single crystal is increased during formation of a taperportion of the single crystal in an initial stage of growth of thesingle crystal, and the single crystal is cylindrically grown connectingwith the taper portion during formation of a straight body portion ofthe single crystal, while the radiation heat toward an upper portionabove the upper end portion of the crucible is blocked during theformation of the straight body portion of the single crystal and,thereby, the above-described problems are solved.

An apparatus for producing a single crystal of the present invention isconfigured to comprise a straight body portion radiation heat blockingmember which can pass through a single crystal and which blocks theradiation heat from the upper end portion of the crucible toward anupper portion and a straight body portion radiation heat blocking membertransporting device for transporting the straight body portion radiationheat blocking member in a vertical direction, while a heating deviceheats a portion in the side lower than the upper end portion of thecrucible, and the straight body portion radiation heat blocking membertransporting device transports the straight body portion radiation heatblocking member to the position at a distance from the upper end portionof the crucible during formation of a taper portion of the singlecrystal to increase the diameter of the single crystal in an initialstage of growth of the single crystal and positions the straight bodyportion radiation heat blocking member in between the outer perimetersurface of the straight body portion of the single crystal and the innerperimeter surface of the crucible or in between the outer perimetersurface of the straight body portion of the single crystal and the upperend portion of the crucible during formation of the straight bodyportion of the single crystal cylindrically grown connecting with thetaper portion and, thereby, the above-described problems are solved.

In this manner, during the formation of the straight body portion of thesingle crystal, since the heat dissipation from the outer perimetersurface of the straight body portion of the single crystal in thecrucible is reduced by the straight body portion radiation heat blockingmember, the temperature difference in the radius direction of the singlecrystal at the surface of the growth of the single crystal, i.e. at theposition of the liquid level of the melt, can be reduced. On the otherhand, during the formation of the taper portion of the single crystal,since nothing hinders the heat dissipation from the taper surface of thetaper portion, the heat is dissipated from the taper portion toward anupper portion. Therefore, the temperature rise of the taper surface canbe suppressed, and the roughening of the surface can be suppressed byreducing the amount of heating of the portion located higher than theliquid level of the melt in the crucible. Consequently, the occurrenceof defects, cracks, and the like can be reduced, and the fractiondefective can be reduced.

Furthermore, in the configuration, when a heating device is ahigh-frequency generation device including a high-frequency coil whichis wound around the crucible while the axis is set in a verticaldirection and which is energized by a high-frequency current, and theradiation heat blocking member which can pass through the single crystaland which blocks the radiation heat from the upper end portion of thecrucible toward an upper portion is made of a metal. In this manner, theheat dissipation from the outer perimeter of the straight body portionof the single crystal is further reduced, and the temperature differencein the radius direction of the single crystal at the surface of thegrowth of the single crystal, i.e. at the position of the liquid levelof the melt, can be further reduced.

An apparatus for producing a single crystal of the present invention isconfigured to comprise a crucible for holding a raw material, ahigh-frequency generation device including a high-frequency coildisposed surrounding the crucible, and a crystal transporting device forrotating and transporting a seed crystal upwards from the inside of thecrucible, wherein the apparatus for producing a single crystal includesa wall-side heating member for heating a portion in between the upperend portion and the lower end portion of the side wall of the crucibleby the operation of the high-frequency generation device and, thereby,the above-described problems are solved.

By adopting such a configuration, when the wall-side heating member isincluded, the portion in between the upper end portion and the lower endportion of the crucible is also heated in addition to the upper endportion and the lower end portion of the crucible and, therefore, thetemperature distribution of the side wall of the crucible can beuniformed. As a result, the convection of the melt which rises along theside wall of the crucible toward the liquid level can be effected, andthe melt in the crucible can be prevented from exhibiting an undesiredconvection pattern. Consequently, the solid-liquid interface portion ofthe single crystal can be flattened regardless of conditions, e.g., thesize and the shape of the crucible, the occurrence of defects, cracks,and the like can be reduced, and the fraction defective can be reduced.

An apparatus for producing a single crystal of the present invention isconfigured to include a bottom-side heating member for heating a centralportion of the bottom by the operation of the high-frequency generationdevice, on the bottom of the crucible and, thereby, the above-describedproblems are solved.

By adopting such a configuration, when the bottom-side heating member isincluded, the central portion of the bottom is heated in addition to thelower end portion, i.e. the periphery of the bottom of the crucible.Therefore, the convection of the melt can be effected, wherein the meltrises from the central portion of the bottom of the crucible toward thesolid-liquid interface portion of the seed crystal or the singlecrystal, impinges on the solid-liquid interface portion of the seedcrystal or the single crystal, and spreads in the radius direction and,thereby, the melt in the crucible can be prevented from exhibiting anundesired convection pattern. Consequently, the solid-liquid interfaceportion of the single crystal can be flattened regardless of conditions,e.g., the size and the shape of the crucible, the occurrence of defects,cracks, and the like can be reduced, and the fraction defective can bereduced.

In the configuration, the wall-side heating member is composed of aprotrusion-shaped member which is made of an electrically conductivematerial and which is disposed in between the upper end portion and thelower end portion of the outer surface of the side wall of the cruciblewhile being extended along the circumferential direction of the outersurface of the side wall of the crucible. By adopting such aconfiguration, an electromagnetic field generated by the high-frequencycoil concentrates on a pointed corner portion close to thehigh-frequency coil. Consequently, the wall-side heating member formedfrom the protrusion-shaped member also generates heat in addition to theupper end portion and the lower end portion of the crucible due to theelectromagnetic field generated by the high-frequency coil, and theportion in between the upper end portion and the lower end portion ofthe crucible can be heated.

Furthermore, in the configuration, the bottom-side heating member iscomposed of a heat conducting portion made of a heat conductive materialfor conducting heat to a central portion of the outer surface of thebottom of the crucible and a board-shaped heat generation portion whichhas a diameter larger than the diameter of the heat conducting portionand which is made of an electrically conductive material. In theconfiguration, the bottom-side heating member is composed of a heatinsulating member made of a heat insulating material having a throughhole serving as a heat conducting portion at the position in accordancewith the central portion of the outer surface of the bottom of thecrucible and a board-shaped heat generation portion which has a diameterlarger than the diameter of the through hole of this heat insulatingmember and which is made of an electrically conductive material. Byadopting such a configuration, an electromagnetic field generated by thehigh-frequency coil concentrates on a pointed corner portion close tothe high-frequency coil. Consequently, the periphery of the heatgeneration portion of the bottom-side heating member also generates heatdue to the electromagnetic field generated from the high-frequency coil.Since the heat from this heat generation portion is conducted to thecentral portion of the bottom of the crucible via the heat conductingportion of the bottom-side heating member or the through hole of theheat insulating member, the central portion of the bottom of thecrucible can be heated.

In the configuration, when the heat generation portion is in the shapeof a disk, and the diameter of the heat generation portion is largerthan or equal to two-thirds the diameter of the bottom of the crucible,the periphery of the heat generation portion is allowed to reliablygenerate heat by the high-frequency generation device.

The wall-side heating member and the bottom-side heating member areconfigured to be attached to the crucible while being attached anddetached at will. Furthermore, in the configuration, a heating membertransporting device is included for transporting the wall-side heatingmember and the bottom-side heating member between the position at whichthe wall-side heating member and the bottom-side heating member are incontact with the crucible and the position at which the wall-sideheating member and the bottom-side heating member are at a distance fromthe crucible. By adopting such a configuration, the wall-side heatingmember and the bottom-side heating member are attached to or detachedfrom the crucible in accordance with, for example, the stage of theformation of the single crystal, and the heating of the side wall andthe bottom of the crucible by the wall-side heating member and thebottom-side heating member can be selected as needed.

In the formation of a single crystal by the use of the apparatus forproducing a single crystal comprising the high-frequency generationdevice including the high-frequency coil and the crystal transportingdevice for rotating and transporting a seed crystal upwards from theinside of the above-described crucible, when the single crystal isformed by a method in which at least one of the portion in between theupper end portion and the lower end portion of the side wall of thecrucible and a central portion of the bottom of the crucible is heated,the distribution of heating of the melt in the crucible can becontrolled and, thereby, the quality of the formed single crystal can beimproved.

A single crystal which is produced by any one of the above-describedapparatuses for producing a single crystal or methods for producing asingle crystal can be improved in its quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view showing the schematic configurationof a first embodiment of the apparatus for producing a single crystal,according to the present invention, under the condition of coolingprocess.

FIG. 2 is a vertical sectional view showing the schematic configurationof the first embodiment of the apparatus for producing a single crystal,according to the present invention, under the condition of a formationprocess.

FIG. 3 is a vertical sectional view showing a modified example of theapparatus for producing a single crystal of the first embodiment.

FIG. 4 is a vertical sectional view showing the schematic configurationof a second embodiment of the apparatus for producing a single crystal,according to the present invention, under the condition of a formationprocess.

FIG. 5 is a vertical sectional view showing the schematic configurationof a third embodiment of the apparatus for producing a single crystal,according to the present invention, under the condition of forming ataper portion in a formation process.

FIG. 6 is a perspective view of the vicinity of a crucible forexplaining the arrangement of a radiation heat blocking tube during theformation of a taper portion of a single crystal.

FIG. 7 is a vertical sectional view of the apparatus for producing asingle crystal shown in FIG. 5, under the condition of forming astraight body portion in the formation process.

FIG. 8 is a vertical sectional view showing the schematic configurationof a fourth embodiment of the apparatus for producing a single crystal,according to the present invention, under the condition of forming ataper portion in a formation process.

FIG. 9 is a vertical sectional view showing the condition in thevicinity of a crucible during formation of a straight body portion inthe fourth embodiment.

FIG. 10 is a vertical sectional view of the vicinity of a crucible,showing the schematic configuration of a fifth embodiment of theapparatus for producing a single crystal, according to the presentinvention, under the condition of forming a taper portion in a formationprocess.

FIG. 11 is a vertical sectional view of the vicinity of a crucibleshowing the schematic configuration of a fifth embodiment of theapparatus for producing a single crystal, according to the presentinvention, under the condition of a straight body portion in a formationprocess.

FIG. 12 is a vertical sectional view showing the schematic configurationand the operation of a sixth embodiment of the apparatus for producing asingle crystal, according to the present invention, in a stage offormation of a taper portion of a single crystal.

FIG. 13 is a vertical sectional view showing the schematic configurationand the operation of the sixth embodiment of the apparatus for producinga single crystal, according to the present invention, in a stage offormation of a straight body portion of the single crystal.

FIG. 14 shows a comparison of distributions of heating values in theheight direction of side walls of the apparatus for producing a singlecrystal of the sixth embodiment and a known apparatus for producing asingle crystal.

FIG. 15 shows a comparison of temperature distributions in the heightdirection of side walls of the apparatus for producing a single crystalof the sixth embodiment and a known apparatus for producing a singlecrystal.

FIG. 16 shows the state of convection of a melt in a crucible in a knownapparatus for producing a single crystal.

FIG. 17 is a vertical sectional view showing the schematic configurationand the operation of a seventh embodiment of the apparatus for producinga single crystal, according to the present invention, in a stage offormation of a taper portion of a single crystal.

FIG. 18 shows a comparison of temperature distributions of the bottomsof the apparatus for producing a single crystal of the seventhembodiment and a known apparatus for producing a single crystal.

FIG. 19 is a sectional view showing a modified example of the seventhembodiment of the apparatus for producing a single crystal, according tothe present invention.

FIG. 20 is a sectional view showing another modified example of theseventh embodiment of the apparatus for producing a single crystal,according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

The first embodiment of a technology of producing a single crystal,according to the present invention, will be described below withreference to FIG. 1 and FIG. 2. FIG. 1 is a vertical sectional viewshowing the schematic configuration of an apparatus for producing asingle crystal, according to the present invention, under the conditionof cooling process. FIG. 2 is a vertical sectional view showing theschematic configuration of the apparatus for producing a single crystal,according to the present invention, under the condition of formationprocess.

The apparatus for producing a single crystal of the present embodimentis an apparatus for producing a single crystal having a melting point ofat least 1,500° C., for example. As shown in FIG. 1 and FIG. 2, theapparatus is provided with, for example, a cylindrical crucible 1, acylindrical heat conducting member 3 which surrounds the outer surfaceof a side wall 1 a of the crucible 1 and which has a height larger thanthe height of the crucible 1, a radiation heat blocking member 7 servingas a disk-shaped interface portion radiation heat blocking member whichis disposed at the upper end portion of the heat conducting member 3 andwhich has an opening 5 in a central portion, a refractory 9 surroundingthe outside of the heat conducting member 3, a high-frequency generationdevice including a high-frequency coil 11 which generates highfrequencies in the outside of the refractory 9, and a crystaltransporting device which includes a rod-shaped or band-shaped seedholder 17 for holding a seed crystal 13 and a formed single crystal 15and which rotates and pulls up the crystal held by the seed holder 17toward an upper portion.

The crucible 1 is a cylindrical vessel in which the upper end is openedand the lower end is blocked to form a bottom 1 b, and which is formedfrom an electrically conductive, high-melting point metallic material,e.g., iridium, platinum, tungsten, or molybdenum. The heat conductingmember 3 is formed from a heat conductive material, e.g., high thermalconductivity alumina, ceramic, or iridium. The heat conducting member 3is in the shape of a cylinder in which the upper end and the lower endare opened and the inner diameter is equal to the outer diameter of thecrucible 1 or larger than the outer diameter of the crucible 1, and isdisposed while surrounding the crucible 1 and a space above the crucible1. When the single crystal 15 is held during the cooling process in theproduction of the single crystal, as shown in FIG. 1, the upper end ofthe heat conducting member 3 is located at the position in accordancewith the interface portion between a taper portion 15 a of the singlecrystal 15 which is in the shape of a cone having a diameter graduallybecoming increased, and a straight body portion 15 b which is in theshape of a cylinder formed connecting with the taper portion 15 a.

The radiation heat blocking member 7 serving as an interface portionradiation heat blocking member is in the shape of a disk or a flat-platering in which an opening having a diameter larger than the diameter ofthe straight body portion 15 b of the single crystal 15 is formed in acentral portion, and is formed from a material capable of blocking theradiation heat, e.g., iridium, alumina, ceramic, or zirconia. Theradiation heat blocking member 7 is held at the position in accordancewith the upper end of the heat conducting member 3, i.e., at theposition in accordance with the interface portion between the taperportion 15 a and the straight body portion 15 b of the single crystal 15held during the cooling process in the production of the single crystal,while the periphery is attached to the refractory 9. It is desirablethat the opening disposed in the central portion of the radiation heatblocking member 7 is formed to have a minimum diameter in order to avoidbecoming in contact with the single crystal 15. The material for formingthe radiation heat blocking member 7 may be a heat conductive materialor be a heat insulating material as long as the material can block theradiation heat. However, it is desirable to use the heat insulatingmaterial from the viewpoint of an improvement in capability of blockingthe radiation heat.

The refractory 9 is a cylindrical vessel in which the upper end isopened and the lower end is blocked to form a bottom and which is largerthan the crucible 1 and the heat conducting member 3. The refractory 9is formed from a high-temperature resistant material having anelectrical insulation property and a heat insulation property, e.g., lowthermal conductivity alumina, zirconia, or alumina wool. The height ofthe refractory 9 is larger than the height of the heat conducting member3. The high-frequency generation device is provided with, for example, ahigh-frequency power source not shown in FIG. 1 and FIG. 2, and ahigh-frequency coil 11 electrically connected to the high-frequencypower source with a wire not shown in the drawing. The high-frequencycoil 11 is disposed outside the refractory 9 at the position inaccordance with the side wall 1 a of the crucible 1 while surroundingthe outside of this refractory 9 with the center axis pointing in avertical direction. The crystal transporting device is provided with,for example, the rod-shaped or band-shaped seed holder 17 and a drivingmechanism, although not shown in the drawing, for hanging the seedholder 17 and for rotating and pulling up the seed holder 17.

The crucible 1, the heat conducting member 3, the radiation heatblocking member 7, the refractory 9, the high-frequency coil 11, a partof the seed holder 17, and the like are contained in a vessel 19. Thecrucible 1 is supported on the support member 21 disposed on the bottomsurface of the vessel 19. A through hole 23 is formed in the ceiling ofthe vessel 19 at the position in accordance with the central portion ofthe opening of the crucible 1. The seed holder 17 is inserted throughthis through hole 23 while hanging from an upper portion.

The operation of the apparatus for producing a single crystal havingsuch a configuration and characteristic portions of the presentinvention will be described. A crystal material serving as a rawmaterial for the crystal, e.g., Gd₂SiO₅, Bi₄Ge₃O₁₂, or Lu₂SiO₅ is heldin the crucible 1 and, thereby, a melt 25 is prepared. When ahigh-frequency current is passed from the high-frequency power source,although not shown in the drawing, through the high-frequency coil 11,an induced current passes through the electrically conductive crucible1. In this manner, the crucible 1 is heated by Joule heating, thetemperature of the crucible 1 is raised and, thereby, the melt 25 in thecrucible 1 becomes in a heated state. When the seed crystal 13 held atthe lower end portion of the seed holder 17 is brought into contact withthis melt 25 in this state and is pulled up from the melt 25, the singlecrystal 15 is formed, as shown in FIG. 2. The production of the singlecrystal includes a formation process in which, initially, a taperportion 15 a of the single crystal 15 is formed into the shape of a coneconnecting with the seed crystal 13 and having a diameter graduallybecoming increased and, thereafter, a cylindrical straight body portion15 b is formed connecting with the taper portion 15 a, as shown in FIG.2, and a cooling process in which the formed single crystal 15 in astate of being pulled up is stood while being held by the seed holder 17so as to be cooled, as shown in FIG. 1.

In the formation process shown in FIG. 2, the heat is dissipated fromthe surfaces of the seed crystal 13 and the single crystal 15 toward theceiling of the vessel 19 by the radiative transfer, the formed singlecrystal 15 is further cooled by the heat conduction via the seed crystal13 and the seed holder 17 and, thereby, the temperature becomes lowerthan or equal to the melting point of the crystal material.Consequently, the lower surface of the single crystal 15 in contact withthe melt 25 becomes a growth surface 15 c, and a fresh crystal grows.

At this time, the heat generation of the crucible 1 occurs in both theportion in contact with the melt 25 and the portion located above themelt 25. The heat generated by the heat generation of this crucible 1 isconducted to an upper portion above the crucible 1 by conduction throughthe conductive member 3. Therefore, the temperature at any height in thespace surrounded by the conductive member 3 becomes close to thetemperature of the single crystal 15 immediately after formationcompared with that in the case where the conductive member 3 is notdisposed. Consequently, in the formation process, the heat dissipationfrom the outer perimeter surface of the single crystal 15, which leavesthe crucible 1 towards an upper portion and is cooled, to the spacesurrounding the single crystal 15 in the outside of the crucible 1 bythe radiative transfer is reduced and, thereby, the temperaturedifference in the radius direction of the single crystal 15 is reduced.

On the other hand, in the cooling process, as shown in FIG. 1, thelong-grown single crystal 15 is isolated from the melt 25, and is cooledto room temperature by gradually reducing the amount of heating. In thiscooling process, the adequately long-grown single crystal 15 istransported toward an upper portion, and is isolated from the melt 25.The temperature is lowered by gradually reducing the high-frequencyelectric power generated from the high-frequency coil 11. At this time,as in the formation process, the heat dissipation from the outerperimeter surface of the single crystal 15 to the space surrounding thesingle crystal 15 in the outside of the crucible 1 is reduced by theconduction of the heat due to the heat generation of the crucible 1 tothe conductive member 3.

Furthermore, in the cooling process, since the radiation heat blockingmember 7 is disposed at the position in accordance with the interfaceportion between the taper portion 15 a and the straight body portion 15b of the single crystal 15, the radiation heat blocking member 7performs the function of a lid, and the heat dissipation by theradiative transfer from the interface portion between the taper portion15 a and the straight body portion 15 b of the single crystal 15 towardan upper portion is reduced. A relatively-low-temperature gas at theceiling portion and the like in the vessel 19 is resistant to flowdownwards into a portion below the interface portion between the taperportion 15 a and the straight body portion 15 b of the single crystal15. Therefore, only the straight body portion 15 b of the single crystal15 is thermally insulated, and a condition in which only the heatdissipation from the straight body portion 15 b of the single crystal 15is reduced is brought about. In this manner, the temperature differencein the radius direction of the straight body portion 15 b of the singlecrystal 15 is reduced.

In general, in the cooling process, since the heat generation of thecrucible 1 is small in contrast to that in the formation process, thetemperature difference in the radius direction of the single crystal,i.e. a nonuniform temperature distribution, tends to occur. However, inthe present embodiment, the action of the conductive member 3 and theaction of the radiation heat blocking member 7 are combined and,thereby, the heat dissipation from the outer perimeter surface of thestraight body portion 15 b of the single crystal 15 is reduced in thecooling process, and the temperature difference in the radius directionis reduced. Furthermore, in the taper portion 15 a of the single crystal15, the heat is dissipated by the radiative transfer from the tapersurface of the taper portion 15 a and the convective heat transfer dueto the flow of the relatively-low-temperature gas in the vessel 19 tothe taper surface of the taper portion 15 a and, thereby, the singlecrystal 15 can be cooled at an appropriate cooling rate. A temperaturegradient having a constant linear temperature distribution occurs in avertical direction, i.e. in a longitudinal direction, of the singlecrystal 15 due to the heat dissipation from the taper surface of thetaper portion 15 a. However, since the thermal stress due to thistemperature gradient, i.e. the temperature difference, in thelongitudinal direction is small, defects, cracks, and the like areresistant to occur due to this temperature difference in thelongitudinal direction.

As described above, in the apparatus for producing a single crystal andthe method for producing a single crystal of the present embodiment, theheat conducting member 3 is comprised, and when the single crystal 15leaving the crucible 1 is cooled, the heat of the crucible 1 isconducted by the heat conducting member 3 to the space located outsideand above the crucible 1 and surrounded by the heat conducting member 3and, thereby, the amount of the heat dissipated from the outer perimetersurface of the single crystal 15 is reduced. Consequently, thetemperature difference in the radius direction of the single crystal 15is reduced. Therefore, the occurrence of defects, cracks, and the likecan be reduced, and the fraction defective can be reduced in theproduction of the single crystal.

Furthermore, in the apparatus for producing a single crystal and themethod for producing a single crystal of the present embodiment, sincethe radiation heat blocking member 7 for blocking the radiation heattoward an upper portion above the interface portion between the taperportion 15 a and the straight body portion 15 b of the single crystal 15is comprised, when the single crystal 15 is cooled in the coolingprocess, the heat dissipation from the outer perimeter surface of thestraight body portion 15 b of the single crystal 15 by the radiativetransfer is blocked and, in addition, the flow of arelatively-low-temperature gas from the vicinity of the ceiling in thevessel 19 into the space surrounding the outer perimeter surface of thestraight body portion 15 b of the single crystal 15 is blocked.Consequently, the temperature difference in the radius direction in thestraight body portion 15 b of the single crystal 15 is reduced.Furthermore, only the taper surface of the taper portion 15 a of thesingle crystal 15 is cooled so as to linearize the temperaturedistribution in the longitudinal direction of the single crystal 15 and,thereby, the cooling rate can be maintained. Therefore, the occurrenceof defects, cracks, and the like can be reduced, and the fractiondefective can be reduced in the production of the single crystal.

In addition, in the apparatus for producing a single crystal and themethod for producing a single crystal of the present embodiment, sincethe heat conducting member 3 is comprised together with the radiationheat blocking member 7, the effect of heat-insulating the straight bodyportion 15 b of the single crystal 15 can be improved in the coolingprocess, the occurrence of defects, cracks, and the like can be furtherreduced, and the fraction defective can be further reduced in theproduction of the single crystal.

That the occurrence of defects, cracks, and the like can be furtherreduced refers to that dropouts of crystal can be reduced while thedropouts lead to defects and cracks. Since dropouts of crystal in theproduct of single crystal can be reduced, the quality of the product ofsingle crystal can also be improved.

In the known technology of forming a single crystal, the radiation heatreflector is disposed at the position immediately above the singlecrystal, the lid is disposed on the upper portion of the refractory inthe cooling process, or the lid is disposed on the upper portion of thecrucible. Consequently, the cooling time is increased in the formationprocess or the cooling process, the growth rate of the single crystal inthe formation process is reduced and, in addition, the cooling time ofthe single crystal is increased in the cooling process. Therefore, aproblem occurs in that the production capacity is reduced.

In contrast to this, with respect to the technology of producing asingle crystal of the present embodiment, there is no member serving asa lid in the condition of the formation process, and the heat can bedissipated from the taper portion of the single crystal in the conditionof the cooling process. Consequently, the growth rate of the singlecrystal is resistant to be reduced in the formation process, and thecooling time is resistant to be increased in the cooling process.Therefore, a reduction in the production capacity can be suppressed.

In the present embodiment, the disk-shaped radiation heat blockingmember 7 which was disposed at the upper end portion of the heatconducting member 3 and which had an opening 5 in the central portionwas shown as the interface portion radiation heat blocking member.However, the interface portion radiation heat blocking member is notlimited to have such a configuration, and can have variousconfigurations as long as the interface portion radiation heat blockingmember is disposed at the position in accordance with the interfaceportion between the straight body portion and the taper portion of thesingle crystal and can block the radiation heat towards an upperportion. For example, as shown in FIG. 3, in the configuration, theupper end portion of the refractory 9 may be set at the position inaccordance with the interface portion between the taper portion 15 a andthe straight body portion 15 b of the single crystal 15, and a lidportion 9 a may be formed as the interface portion radiation heatblocking member on this upper end portion of the refractory 9 whileprotruding in the shape of a ring toward the single crystal from thisupper end portion.

At this time, since the refractory 9 has a certain thickness, the lowersurface of the lid portion 9 a of the refractory 9 is set at theposition in accordance with the interface portion between the taperportion 15 a and the straight body portion 15 b of the single crystal15, and an opening 9 b formed in the central portion of the lid portion9 a is made to be a taper-shaped opening having a diameter graduallybecoming increased with height. In this manner, the radiation heattoward an upper portion above the interface portion between the taperportion 15 a and the straight body portion 15 b of the single crystal 15can be blocked and, in addition, the taper portion 15 a of the singlecrystal 15 can be prevented from being heat-insulated by beingsurrounded by the lid portion 9 a of the refractory 9 having a certainthickness.

In the present embodiment, the cylindrical heat conducting member 3which surrounded the outer surface of the side wall 1 a of the crucible1 and which had a height larger than the height of the crucible 1 wasshown as the heat conducting member. However, the heat conducting memberis not limited to have such a configuration, and can have variousconfigurations as long as the heat conducting member can conduct theheat of the crucible 1 or the vicinity of the crucible 1 toward an upperportion. For example, as shown in FIG. 3, the lower end portion of theheat conducting member may be positioned in the vicinity of the upperend portion of the crucible 1, and the upper end portion of the heatconducting member may be positioned at some midpoint of the height ofthe straight body portion 15 b of the single crystal 15 in the coolingprocess. As described above, the heat conducting member is notnecessarily in contact with the crucible 1, nor surrounds the crucible1. The height can also be appropriately selected depending on theconditions, for example, whether the interface portion radiation heatblocking member is disposed or not.

In the configuration shown in the present embodiment, both the radiationheat blocking member 7 serving as the interface portion radiation heatblocking member and the heat conducting member 3 were disposed. However,the effect of the present invention can be achieved even when any one ofthe interface portion radiation heat blocking member and the heatconducting member is disposed. Here, an example will be shown, in whichthe effect was calculated by numerical simulations with respect to thecase where the interface portion radiation heat blocking member wasdisposed alone. The temperature distribution in the crystal wascalculated on the case where the radiation heat blocking member 7 asshown in FIG. 1 was disposed or not disposed under the calculationcondition that the crystal material was Gd₂SiO₅ having a melting pointof 1,950° C. As a result of the calculation, the temperature differencein the radius direction at the height of the central portion of thesingle crystal 15 in the cooling process was on the order of 50° C. inthe case where the radiation heat blocking member 7 was not disposed,and was on the order of 35° C. in the case where the radiation heatblocking member 7 was disposed. In this manner, even when the interfaceportion radiation heat blocking member is disposed alone, thetemperature difference in the radius direction of the single crystal inthe cooling process can be reduced, cracks and the like due to thethermal stress can be prevented and, thereby, a reduction of thefraction defective, an improvement in the quality, and the like can beachieved. However, when both the interface portion radiation heatblocking member and the heat conducting member are disposed, theseeffects can be improved compared with the effects exhibited when any oneof them is disposed.

Second Embodiment

The second embodiment of the technology of producing a single crystal,according to the present invention, will be described below withreference to FIG. 4. FIG. 4 is a vertical sectional view showing theschematic configuration of an apparatus for producing a single crystal,according to the present invention, under the condition of formationprocess. In the present embodiment, the same elements and operations asthose in the first embodiment are indicated by the same referencenumerals as in the first embodiment, explanations thereof will not beprovided, and configurations, characteristic portions, and the likedifferent from those in the first embodiment will be described.

The technology of producing a single crystal of the present embodimentis different from the first embodiment in the point that the interfaceportion radiation heat blocking member can be transported in a verticaldirection. As shown in FIG. 4, an apparatus for producing a singlecrystal of the present embodiment is provided with, for example, a diskring-shaped radiation heat blocking member 29 including a through hole27 in accordance with the diameter of a straight body portion 15 b of asingle crystal 15 in a central portion and an interface portionradiation heat blocking member transporting device for supporting theradiation heat blocking member 29 and, in addition, for transporting itin a vertical direction. The radiation heat blocking member 29 servingas the interface portion radiation heat blocking member with thesurfaces of the disk facing in a vertical direction is supported by arod-shaped support member constituting the interface portion radiationheat blocking member transporting device. The interface portionradiation heat blocking member transporting device supports theradiation heat blocking member 29 and is composed of, for example, therod-shaped support member 31 which is inserted through a through holedisposed in the ceiling of a vessel 19 and which is extended in avertical direction and a transporting mechanism, although not shown inthe drawing, disposed in the outside of the vessel 19 to transport thesupport member 31 in the vertical direction.

In the present embodiment described above, the radiation heat blockingmember 29 is located at the position in accordance with the interfaceportion between the taper portion 15 a and the straight body portion 15b of the single crystal 15 in the formation process as well as in thecooling process, and is transported upwards with the growth of thesingle crystal 15. As a result, in both the formation process and thecooling process, the temperature difference in the radius direction ofthe single crystal 15 is reduced by the action of the radiation heatblocking member 29, and the fraction defective can be reduced in theproduction of the single crystal.

Furthermore, the effects of improving the quality and improving theproduction capacity can also be achieved.

Such an operation that the radiation heat blocking member 29 is isolatedfrom the single crystal 15 and a refractory 9 and is transported to anupper portion of the apparatus in the formation process, and theradiation heat blocking member 29 is positioned at the interface portionof the single crystal 15 in only the cooling process can also beperformed depending on the conditions, e.g., the type of single crystalto be produced. In this case, since there is no radiation heat blockingaction by the radiation heat blocking member 29 in the formationprocess, the growth rate can be increased by the heat dissipation fromthe surroundings of the single crystal 15, and the temperaturedistribution in the radius direction of the single crystal 15 can beuniformed in only the cooling process. The temperature difference in theradius direction of the crystal occurs in the formation process of thesingle crystal 15 depending on the conditions, e.g., the type of singlecrystal to be produced. Fluidity is exhibited as the property of thematerial for the crystal depending on the conditions, e.g., the type ofsingle crystal to be produced. However, when the temperature becomesclose to the melting point, thereby, defects, cracks, and the like maybe resistant to occur.

Third Embodiment

The third embodiment of the technology of producing a single crystal,according to the present invention, will be described below withreference to FIG. 5 to FIG. 7. FIG. 5 is a vertical sectional viewshowing the schematic configuration of an apparatus for producing asingle crystal, according to the present invention, under the conditionof formation of a taper portion in a formation process. FIG. 6 is aperspective view of the vicinity of a crucible for explaining thearrangement of a radiation heat blocking tube during the formation ofthe taper portion of the single crystal. FIG. 7 is a vertical sectionalview of the apparatus for producing a single crystal shown in FIG. 5,under the condition of forming a straight body portion in the formationprocess. In the present embodiment, the same elements and operations asthose in the first and the second embodiments are indicated by the samereference numerals as in those embodiments.

As shown in FIG. 5, the apparatus for producing a single crystal of thepresent embodiment is configured to include a cylindrical vessel 19which is disposed with an axis line being set in vertical direction andwhich has a rectangular vertical cross section, a refractory 9 which isa cylindrical heat insulating material supported by a support member 21on the upper surface of a bottom 19 a of the vessel 19 and which isdisposed concentrically with the vessel 19, a crucible 1 disposedconcentrically with the refractory 9, on a bottom 9 c of the refractory9, a crystal transporting device including a rod-shaped or band-shapedseed holder 17 which is inserted through an opening formed in a centralportion of an upper surface 19 b of the vessel 19 and which is disposedwhile being allowed to vertically move along a center line of therefractory 9, a seed crystal 13 attached to the lower end of the seedholder 17, a radiation heat blocking tube 33 serving as an in-crucibleradiation heat blocking member disposed concentrically with therod-shaped or band-shaped seed holder 17 and configured to be allowed tovertically move along the center line of the refractory 9, a radiationheat blocking tube transporting device serving as an in-crucibleradiation heat blocking member transporting device which is insertedthrough an opening formed in the central portion of the upper surface 19b of the vessel 19 and which vertically transports the radiation heatblocking tube 33 along the center line of the refractory 9, and ahigh-frequency coil 11 for high-frequency induction heating of thecrucible 1, the coil being wound around the outer perimeter of the lowerportion of the refractory 9, concentrically with the refractory 9.

The vessel 19 is in the shape of a cylinder with the top and the bottombeing closed, and the upper surface 19 b is provided with theabove-described opening for passing through the seed holder 17 and anopening for passing through a support member 35 of the rod-shapedradiation heat blocking tube 33 included in the radiation heat blockingtube transporting device. The refractory 9 is in the shape of a cylinderin which the lower end is closed with the bottom 9 c and the upperportion is opened. The high frequency coil 11 is wound around from thelower end portion of the refractory 9 up to the position higher than theposition of the outer perimeter surface of the refractory 9, inaccordance with the upper end portion of the crucible 1 in order to heatthe entire crucible 1. The crucible 1 is filled in with a melt 25serving as a material for a single crystal to such an extent that theliquid level reaches a position somewhat lower than the upper end of thecrucible 1.

The radiation heat blocking tube 33 is formed from a nonmetallicmaterial, e.g., the same material as the crystal material, and as shownin FIG. 6, is in the shape of a short tube having the inner diameterlarger than or equal to the diameter of a straight body portion of aproduct single crystal. The crystal transporting device is composed of,for example, the seed holder 17 and a transporting mechanism, althoughnot shown in the drawing, for transporting the seed holder 17 in avertical direction. Likewise, the in-crucible radiation heat blockingmember transporting device is composed of, for example, the supportmember 35 and a transporting mechanism, although not shown in thedrawing, for transporting the support member 35 in a vertical direction.

The operation of the apparatus for producing a single crystal havingsuch a configuration and characteristic portions of the presentinvention will be described. High-frequency waves are generated in thevicinity of the crucible 1 by energizing the high-frequency coil 11, andthe crucible 1 made of a metal generates heat. The temperature of thecrucible 1 is increased and, therefore, the temperature of the melt 25of the crystal material is increased. The lower end portion of the seedcrystal 13 is brought into contact with the melt 25, and the melt 25brought into contact with the seed crystal 13 is cooled by heatconduction via the seed crystal 13 and the seed holder 17. Since thetemperature of the seed crystal 13 is lower than or equal to the meltingpoint of the crystal material, a fresh crystal, i.e. a single crystal15, grows on the surface of the seed crystal 13 in contact with the melt25. As the fresh crystal grows, the seed crystal 13 is pulled up towardan upper portion with the seed holder 17. The heat is dissipated fromthe surfaces of the seed crystal 13 and the single crystal 15 toward theceiling portion of the vessel 19 and the inner surface of the refractory9 by the radiative transfer, and cooling is performed by the heatconduction via the seed crystal 13 and the seed holder 17, so that thetemperature of the single crystal 15 becomes lower than or equal to themelting point of the crystal material. Consequently, a fresh crystalgrows on the surface of the single crystal 15 in contact with the melt25.

As shown in FIG. 5, during the formation of a taper portion in aninitial stage of growth of the single crystal, a taper portion 15 a inthe shape of a conically divergent taper is formed on the surface of theupper portion of the single crystal 15 in order that the diameter of theseed crystal 15 is gradually increased. At this stage, in order toprevent the taper surface of the taper portion 15 a from directly facingthe crucible inner surface 37 located higher than the liquid level ofthe melt 25, the radiation heat blocking tube 33 is transportedconcentrically with the seed crystal 13 and the seed holder 17, anddisposed at the position in between the crucible inner surface 37 andthe taper surface of the taper portion 15 a of the single crystal 15.The length of the radiation heat blocking tube 33 in the axis directionis set at a length that can prevent the radiation heat from the crucibleinner surface 37 from reaching the taper surface of the taper portion 15a, from the highest portion of the taper surface of the taper portion 15a to the lowest portion of the taper surface of the taper portion 15 a,even when the liquid level of the melt 25 reaches the lowest levelduring the formation of the taper portion.

The heat generation of the crucible 1 occurs in both the portion incontact with the melt 25 and the portion located higher than the melt25. However, during the formation of the taper portion shown in FIG. 5,since the radiation heat from the crucible inner surface 37 at a hightemperature to the taper surface of the taper portion 15 a is blocked bythe radiation heat blocking tube 33, the taper surface of the taperportion 15 a can be maintained at a low temperature and, therefore, thesurface roughening of the taper surface due to thermal etching does notoccur. The radiation heat blocking tube 33 is made of a nonmetallicmaterial and, therefore, is not susceptible to high-frequency heating.

When the diameter of the single crystal 15 is increased and reaches apredetermined size, as shown in FIG. 7, the formation of the taperportion 15 a is terminated, and the formation of the straight bodyportion is performed. In the formation of the straight body portion, thesingle crystal is long-formed into the shape of a cylinder and, thereby,the straight body portion 15 b is formed. At this time, the radiationheat blocking tube 33 is isolated from the crucible 1 and the singlecrystal 15, and is transported to the upper portion of the vessel 19, sothat the outer perimeter surface of the straight body portion 15 b ofthe single crystal 15 directly faces the crucible inner surface 37.

As shown in FIG. 7, since the radiation heat blocking tube 33 istransported to the upper portion when the formation of the straight bodyportion is started, the outer perimeter surface of the straight bodyportion 15 b of the single crystal 15 directly faces the crucible innersurface 37 at a high temperature, and is heated by the radiation heat ofthe crucible inner surface 37. Since the amount of heating thereofcancels the amount of heat dissipated from the outer perimeter surfaceof the straight body portion 15 b of the single crystal 15 to theceiling portion of the vessel 19 and the refractory 9, the temperaturedifference in the radius direction of the single crystal 15 is reduced,and a crystal grows uniformly on the surface 15 c of the single crystal15 in contact with the melt 25. During the formation of the straightbody portion, since the heat dissipated from a crystal portion locatedabove the crucible 1, i.e. the taper surface of the taper portion 15 a,is large, even when a portion of the outer perimeter surface of thestraight body portion 15 b of the single crystal 15 is located in thecrucible and directly faces the crucible inner surface 37, a hightemperature does not result, and the surface roughening due to thermaletching does not occur on the outer perimeter surface of the straightbody portion 15 b. By these actions, the fraction defective can bereduced without occurrence of fractures, i.e. cracks, or the like, and asingle crystal having an improved quality can grow.

The effect of the present embodiment was calculated by numericalsimulations. The temperature change was calculated depending on thepresence or absence of the radiation heat blocking tube 33 serving asthe in-crucible radiation heat blocking member in the formation of thetaper portion, as in the present embodiment shown in FIG. 5 and FIG. 7,under the calculation condition that the crystal material was Gd₂SiO₅having a melting point of 1,950° C. The temperature of the crystalgrowth surface of the lower portion of the crystal is assumed to be themelting point of 1,950° C. As a result of the calculation, when theradiation heat blocking tube 33 is disposed during the formation of thetaper portion, as shown in FIG. 5, the temperature of the taper surfaceof the taper portion 15 a becomes about 1,730° C. At this time, thereflectance of the radiation heat blocking tube 33 is assumed to be 1.0.Provided that the radiation heat blocking tube 33 is not disposed, thetemperature of the taper surface of the taper portion 15 a becomes about1,780° C. Therefore, the presence or absence of the radiation heatblocking tube, i.e. the in-crucible radiation heat blocking member,results in the difference in the temperature of the taper surface on theorder of 50° C.

As described above, according to the technology of producing a singlecrystal of the present embodiment, the taper surface temperature can belowered during the formation of the taper portion, roughening of thesurface thereof due to thermal etching can be reduced, and theoccurrence of defects, cracks, and the like originated in the tapersurface can be reduced. Consequently, the fraction defective can bereduced in the production of the single crystal.

Furthermore, in the present embodiment, growth can be performeduniformly in a crystal surface during the formation of the straight bodyportion of the crystal, and the growth rate can be increased. Inaddition, the present invention also exhibits the effect of improvingthe controllability of the crystal growth.

Fourth Embodiment

The fourth embodiment of the technology of producing a single crystal,according to the present invention, will be described below withreference to FIG. 8 and FIG. 9. FIG. 8 is a vertical sectional viewshowing the schematic configuration of the apparatus for producing asingle crystal, according to the present invention, under the conditionof forming a taper portion in a formation process. FIG. 9 is a verticalsectional view showing the condition in the vicinity of a crucibleduring formation of a straight body portion in the present embodiment.In the present embodiment, the same elements and operations as those inthe third embodiment are indicated by the same reference numerals as inthe third embodiment, explanations thereof will not be provided, andconfigurations, characteristic portions, and the like different fromthose in the third embodiment will be described.

The present embodiment is different from the third embodiment in thepoint that a ring-shaped straight body portion radiation heat blockingmember made of the same metallic material as that of a crucible and astraight body portion radiation heat blocking member transporting devicefor transporting the straight body portion radiation heat blockingmember along the center line of a refractory in a vertical direction aredisposed in place of the radiation heat blocking tube transportingdevice and the radiation heat blocking tube. As shown in FIG. 8, anapparatus for producing a single crystal, according to the presentembodiment, is provided with, for example, a radiation heat shieldingplate 39 serving as the ring-shaped straight body portion radiation heatblocking member made of the same metallic material as that of a crucible1 and the straight body portion radiation heat blocking membertransporting device for transporting the radiation heat shielding plate39 along the center line of a refractory 9 in a vertical direction.

The straight body portion radiation heat blocking member transportingdevice is composed of, for example, a rod-shaped support member 41 forsupporting the radiation heat shielding plate 39 and a transportingmechanism, although not shown in the drawing, for transporting thesupport member 41 in the vertical direction. An entire high-frequencycoil 11 is lowered downwards compared with that in the third embodimentin order that an upper end portion thereof becomes lower than an upperend portion of the crucible 1 and, therefore, the amount of heating ofthe portion located higher than the liquid level of a melt 25 in thecrucible 1 is smaller than that in the third embodiment.

The radiation heat shielding plate 39 is located at the position higherthan the upper end of the refractory 9 during the formation of the taperportion of the single crystal 15, and is located around the singlecrystal in an upper portion of the crucible 1 during the formation ofthe straight body portion of the single crystal 15. The radiation heatshielding plate 39 has an outer diameter substantially equal to orsmaller than the inner diameter of the crucible 1 and an inner diameterslightly larger than the outer diameter of the straight body portion 15b of the formed single crystal 15.

The crucible 1 is heated by energizing the high-frequency coil 11.However, with respect to this heating, since the entire high-frequencycoil 11 is lowered downwards compared with that in the third embodiment,the amount of heating of the portion located higher than the liquidlevel of the melt 25 in the crucible 1 becomes small. In the presentembodiment, as shown in FIG. 8, during the formation of the taperportion of the single crystal 15, the radiation heat shielding plate 39is transported above the upper portion in the vessel 19 and the upperend of the refractory 9 by the straight body portion radiation heatblocking member transporting device including the support member 41.

Thus, during the formation of the taper portion, since the radiationheat shielding plate 39 is not present, the heat is dissipated toward anupper portion from the taper surface of the taper portion 15 a of thesingle crystal 15 and, thereby, the taper surface of the taper portion15 a can be maintained at a lower temperature. Although the tapersurface of the taper portion 15 a directly faces the inner surface ofthe crucible 1, since the amount of heating of the portion locatedhigher than the liquid level of the melt 25 in the crucible 1 by thehigh-frequency coil 11 is reduced, the amount of heating is smaller thanthe amount of heat dissipated from the taper surface of the taperportion 15 a, the taper surface of the taper portion 15 a is maintainedat a low temperature, and roughening of the surface due to a hightemperature can be avoided.

After the formation of the taper surface of the taper portion 15 a iscompleted, as shown in FIG. 9, in the process of forming the straightbody portion, the radiation heat shielding plate 39 is lowered downwardsfrom the position shown in FIG. 8, and is disposed around the straightbody portion 15 b of the single crystal 15 in the upper portion of thecrucible 1 in order to block the space between the upper end of thecrucible 1 and the outer perimeter surface of the straight body portion15 b of the single crystal 15. Consequently, the heat dissipation fromthe outer perimeter surface of the straight body portion 15 b of thesingle crystal 15 in the inside of the crucible 1 is reduced, thetemperature difference in the radius direction of the single crystal 15is reduced, the occurrence of defects, cracks, and the like is reduced,and the fraction defective is reduced in the production of the singlecrystal.

Furthermore, a crystal grows uniformly all over the surface 15 c of thesingle crystal 15 in contact with the melt 25. In addition, since nomember blocks the heat dissipation from the taper surface of the taperportion 15 a, the cooling rate of the crystal growth surface isincreased, and a large crystal growth rate can be maintained. Since theradiation heat shielding plate 39 is made of a metal, the temperature ofthe radiation heat shielding plate 39 is increased by high-frequencyheating and, therefore, there is the effect of heating the inside of thecrucible 1.

In FIG. 9, the radiation heat shielding plate 39 is disposed around thestraight body portion 15 b of the single crystal 15 in the upper portionof the crucible 1 in order to block the space between the upper end ofthe crucible 1 and the outer perimeter surface of the straight bodyportion 15 b of the single crystal 15, and this position is desirablebecause suppression of the heat dissipation from the outer perimetersurface of the straight body portion 15 b is maximized. However, evenwhen the radiation heat shielding plate 39 is further lowered and isdisposed at the position in the inside of the crucible 1, thetemperature drop of the outer perimeter surface of the straight bodyportion 15 b at the position close to the liquid level of the melt 25can be suppressed and, therefore, substantially the same effect as thatin the case where the position is as shown in FIG. 9 can be exhibited.

A similar effect can also be exhibited when the radiation heat shieldingplate 39 is made from a ring-shaped member having an inner diameterlarger than the outer diameter of the straight body portion 15 b of thesingle crystal 15 and smaller than the inner diameter of the crucible 1and an outer diameter larger than the outer diameter of the crucible 1,and such a radiation heat shielding plate is located at the positionclose to the upper end portion of the crucible 1 during the formation ofthe single crystal straight body portion and is transported to theposition some distance above the upper end portion of the crucible 1during the formation of the taper portion of the single crystal 15.

Fifth Embodiment

The fifth embodiment of the technology of producing a single crystal,according to the present invention, will be described below withreference to FIG. 10 and FIG. 11. FIG. 10 and FIG. 11 are verticalsectional views of the vicinity of a crucible showing the schematicconfiguration of the apparatus f or producing a single. crystal,according to the present invention, in a formation process. In thepresent embodiment, the same elements and operations as those in thethird and the fourth embodiments are indicated by the same referencenumerals as in the above-described embodiments, explanations thereofwill not be provided, and configurations, characteristic portions, andthe like different from those in the third and the fourth embodimentswill be described.

The present embodiment is different from the third embodiment in thepoint that an in-crucible radiation heat blocking member made of anonmetallic material in the shape of a cone along the tapered shape ofthe taper portion of the single crystal and an in-crucible radiationheat blocking member transporting device for transporting thein-crucible radiation heat blocking member along the center line of arefractory in a vertical direction are disposed in place of theradiation heat blocking tube 33 and the radiation heat blocking tubetransporting device shown in FIG. 5. As shown in FIG. 10, an apparatusfor producing a single crystal, according to the present embodiment, isprovided with a radiation heat shielding plate 43 serving as thein-crucible radiation heat blocking member made of a nonmetallicmaterial in the shape of a cone along the tapered shape of the taperportion 15 a of the single crystal 15 and the in-crucible radiation heatblocking member transporting device which includes a rod-shaped supportmember 45 for supporting the radiation heat shielding plate 43 and whichtransports the radiation heat shielding plate 43 along the center lineof a refractory 9 in a vertical direction. The in-crucible radiationheat blocking member transporting device is composed of, for example, arod-shaped support member 45 which supports the radiation heat shieldingplate 43 and which is extended in a vertical direction and atransporting mechanism, although not shown in the drawing, fortransporting the support member 45 in the vertical direction.

In the present embodiment, as shown in FIG. 10, during the formation ofthe taper portion of the single crystal 15, the radiation heat shieldingplate 43 is positioned close to the taper surface of the taper portion15 a of the single crystal 15. The angle of inclination of the conicalsurface of the radiation heat shielding plate 43 is substantially equalto the angle of inclination of the taper surface of the taper portion 15a. As shown in FIG. 11, during the formation of the straight bodyportion of the single crystal 15, the radiation heat shielding plate 43is transported to the position a distance from the taper surface of thetaper portion 15 a of the single crystal 15.

The operation of the above-described radiation heat shielding plate 43of the present embodiment is similar to the operation of the radiationheat blocking tube 33 in the third embodiment. The radiation heatshielding plate 43 is disposed close to the taper surface of the taperportion 15 a of the single crystal 15 during the formation of the taperportion of the single crystal 15, and the radiation heat shielding plate43 is transported to the position a distance from the taper surface ofthe taper portion 15 a of the single crystal 15 during the formation ofthe straight body portion of the single crystal 15.

In the present embodiment, since the angle of inclination of the conicalsurface of the radiation heat shielding plate 43 is substantially equalto the angle of inclination of the taper surface of the taper portion 15a, the taper portion 15 a is formed during the formation of the taperportion while the spacing between the taper surface of the taper portion15 a and the radiation heat shielding plate 43 is constant at anyposition on the taper surface of the taper portion 15 a. Consequently,the entire surface of the taper surface of the taper portion 15 a can beformed uniformly, an origin of crack, i.e., fracture, is resistant tooccur, and the fraction defective can be reduced in the production ofthe single crystal.

In addition, since the radiation heat shielding plate 43 is not locatedat the position close to the taper surface of the taper portion 15 aduring the formation of the straight body portion, the heat dissipationfrom the taper surface of the taper portion 15 a can be increased and,thereby, the growth rate can be increased.

Therefore, according to the present embodiment as well, the effectssimilar to those in the other embodiments can be exhibited.

The effect of preventing the surface roughening can be exhibited evenwhen not only the conical plate shown in FIG. 10, but also a flat diskis used as the radiation heat shielding plate 43. However, it isdesirable to use a conical plate in accordance with the inclination ofthe taper surface of the taper portion to be formed.

Sixth Embodiment

The sixth embodiment of the apparatus for producing a single crystal,according to the present invention, will be described with reference toFIG. 12 to FIG. 15. FIG. 12 is a vertical sectional view showing theschematic configuration and the operation of an apparatus for producinga single crystal, according to the present invention, in a stage offormation of a taper portion of a single crystal. FIG. 13 is a verticalsectional view showing the schematic configuration and the operation ofthe apparatus for producing a single crystal, according to the presentinvention, in a stage of formation of a straight body portion of thesingle crystal. FIG. 14 shows a comparison of distributions of heatingvalue s in the height direction of side walls of the apparatus forproducing a single crystal, according to the present invention, and aknown apparatus for producing a single crystal. FIG. 15 shows acomparison of temperature distributions in the height direction of sidewalls of the apparatus for producing a single crystal, according to thepresent invention, and a known apparatus for producing a single crystal.In the present embodiment, the same elements, operations, and the likeas those in the first to the fifth embodiments are indicated by the samereference numerals as in the above-described embodiments.

As shown in FIG. 12, an apparatus for producing a single crystal,according to the present embodiment, is composed of, for example, acylindrical crucible 1, ring-shaped members 47 which are attached to anouter surface of the side wall of the crucible 1 and which serve as sidewall heating members, a refractory 9 surrounding the crucible 1,high-frequency generation device 49 which generates high frequencies inthe outside of the refractory 9, and crystal transporting device 51which holds a seed crystal and which rotates and pulls up a crystal.

The apparatus for producing a single crystal of the present embodimentis an apparatus for producing a single crystal having a melting point ofat least 1,500° C. The crucible 1 is a cylindrical vessel in which theupper end portion 1 c is opened and the lower end portion 1 d is blockedto form a bottom 1 b, and which is formed from an electricallyconductive, high-melting point metallic material, e.g., iridium,platinum, tungsten, or molybdenum. The ring-shaped members 47 aredisposed in the shape of a ring on the outer surface of the side wall 1a of the crucible 1 along the circumferential direction of this outersurface of the side wall 1 a, and are protrusion-shaped members in thecondition of protruding in a lateral direction from the outer surface ofthe side wall 1 a.

The above-described ring-shaped member 47 is formed from an electricallyconductive, high-melting point metallic material, e.g., iridium,platinum, tungsten, or molybdenum, similarly to the crucible 1. Thering-shaped members 47 can be formed integrally with the crucible 1, orbe formed separately from the crucible 1, followed by being attached tothe side wall of the crucible 1. When the ring-shaped member 47 isformed separately from the crucible 1, the ring-shaped member 47 may beformed from the same material as the material for forming the crucible1, or be formed from a different material. When the ring-shaped member47 is formed separately from the crucible 1, it is desirable that thering-shaped member 47 is attached while being in contact with thecrucible 1 as strong as possible. In the present embodiment, ring-shapedmembers 47 are disposed on two portions with a spacing, in between anupper end portion 1 c and a lower end portion 1 d of the outer surfaceof the side wall 1 a of the crucible 1.

The refractory 9 is a cylindrical vessel in which the upper end portionis opened and the lower end portion is blocked to form a bottom andwhich is larger than the crucible 1. The refractory 9 is formed from ahigh-temperature resistant material, e.g., zirconia or alumina, havingan electrical insulation property and a heat insulation property, andcontains the crucible 1 provided with the ring-shaped members 47, in theinside. The high-frequency generation device 49 is composed of, forexample, a high-frequency coil 11 and a high-frequency power source 55electrically connected to the high-frequency coil 11 via wires 53. Thehigh-frequency coil 11 is disposed outside the refractory 9 at theposition in accordance with the side wall 1 a of the crucible 1 andsurrounds the outside of this refractory 9. The crystal transportingdevice 51 is composed of, for example, a rod-shaped or band-shaped seedholder 17 and a driving mechanism 57 for hanging the seed holder 17 andfor rotating and pulling up the seed holder 17. The driving mechanism 57supports the seed holder 17 while the seed holder 17 is hung from abovean opening in an upper end portion of the refractory 9 toward a centralportion of an opening of the crucible 1, and the seed crystal 13 isattached to the end portion in the crucible 1 side of the seed holder17.

The operation of the apparatus for producing a single crystal havingsuch a configuration and characteristic portions of the presentinvention will be described. When a high-frequency current is passedfrom the high-frequency power source 55 through the high-frequency coil11 while a raw material is held in the crucible 1, an induced currentpasses through the electrically conductive crucible 1. In this manner,the crucible 1 is heated by Joule heating, the temperature of thecrucible 1 is raised, the raw material in the crucible 1 is melted andbecomes in a molten state, so that a melt 25 is prepared. When the seedcrystal 13 attached to the end portion of the seed holder 17 is pulledup from the melt 25, the single crystal 15 is formed. In the formationof the single crystal 15, initially, a taper portion 15 a is formed intothe shape of a cone connecting with the seed crystal 13 and, as shown inFIG. 13, a cylindrical straight body portion 15 b is formed connectingwith the taper portion 15 a. When the single crystal 15 is pulled upfrom the melt 25, in order to create a flow from the single crystal 15toward the inner surface of the side wall 1 a of the crucible 1, i.e. aflow spreading from the position of the single crystal 15 toward theradius direction, in the vicinity of the liquid level of the melt 25,the seed holder 17 is rotated as a rotation axis and, thereby, thesingle crystal 15 is rotated.

Since an electromagnetic field generated by the high-frequency coil 11particularly concentrates on a corner portion, the upper end portion 1 cand the lower end portion 1 d of the crucible 1 generate a larger amountof heat compared with the other portions. Furthermore, in the presentembodiment, the ring-shaped members 47 disposed in between the upper endportion 1 c and the lower end portion 1 d on the outer surface of theside wall 1 a of the crucible 1 also generate a larger amount of heatcompared with the other portions, similarly to the upper end portion 1 cand the lower end portion 1 d of the crucible 1.

Consequently, as is clear from the heating value distribution 101indicated by a solid line shown in FIG. 14, in the distribution of theheating value of the side wall 1 a per unit volume, peaks are observedat a periphery of the bottom 1 b of the side wall 1 a, i.e. the lowerend portion 1 d, a portion at which the ring-shaped member 47 positionedin the lower side is disposed, a portion at which the ring-shaped member47 positioned in the upper side is disposed, and the upper end portion 1c of the side wall 1 a, in that order from the bottom 1 b of thecrucible 1 toward the upper end portion 1 c, i.e. toward the heightdirection. As a result, in the temperature distribution of the side wall1 a of the crucible 1, as is clear from the temperature distribution 105indicated by a solid line shown in FIG. 15, peaks are observed at aportion of the bottom 1 b of the side wall 1 a, the portion at which thering-shaped member 47 positioned in the lower side is disposed, theportion at which the ring-shaped member 47 positioned in the upper sideis disposed, and the upper end portion 1 c of the side wall 1 a, in thatorder from the bottom 1 b of the crucible 1 toward the upper end portion1 c, i.e. toward the height direction.

On the other hand, with respect to a known apparatus for producing asingle crystal, provided with no ring-shaped member 47, as is clear fromthe heating value distribution 103 indicated by a broken line shown inFIG. 14, in the distribution of the heating value of the side wall perunit volume, peaks are observed only at the periphery of the bottom ofthe side wall, i.e. the lower end portion, and the upper end portion ofthe side wall, in that order from the bottom of the crucible toward theupper end portion, i.e. toward the height direction. As a result, in thetemperature distribution of the side wall of the crucible, as is clearfrom the temperature distribution 107 indicated by a broken line shownin FIG. 15, peaks are observed only at a periphery of the bottom of theside wall and the upper end portion of the side wall, in that order fromthe bottom of the crucible toward the upper end portion, i.e. toward theheight direction. Thus, in the known apparatus for producing a singlecrystal, the heating values and the temperatures of the lower endportion and the upper end portion of the side wall become higher thanthose of the other portions and, therefore, the distributions of theheating value and the temperature are in nonuniform states. As thedistance between the lower end portion and the upper end portion of theside wall are increased, the heating value and the temperature of theportion in between the lower end portion and the upper end portion ofthe side wall are lowered. Consequently, the above-described nonuniformstates of the heating value and the temperature become significantparticularly when a crucible having a height larger than the diameter ofthe bottom or a large crucible having a diameter of the bottom and aheight of at least several tens of centimeters is used.

Therefore, in the known apparatus for producing a single crystal, whenthe distributions of the heating value and the temperature arenonuniform in the height direction of the side wall 1 a and thetemperature of the portion in between the lower end portion 1 d and theupper end portion 1 c of the side wall 1 a is low depending on theconditions, e.g., the size and the shape of the crucible, as shown inFIG. 16, the melt 25 in the crucible 1 expands by being heated at thelower end portion 1 d of the crucible 1, and initially, rises along theinner surface of the side wall 1 a of the crucible 1. However, since thetemperature is lowered at the midpoint of the height of the side wall 1a of the crucible 1, the melt 25 flows away from the side wall 1 a, andconflicts with a flow of the melt 25 in the upper portion in thecrucible 1, so that a complicated convection pattern is exhibited, andthe entire flow of the melt 25 in the crucible 1 is disturbed.

In this manner, the shape of the single crystal formation portion, i.e.the solid-liquid interface portion 59, of the single crystal 15 formedconnecting with the seed crystal 13 is disturbed and becomes in anuneven state. If the shape of the solid-liquid interface portion 59 ofthe single crystal 15 is disturbed and becomes in an uneven state, thequality of the single crystal 15 is deteriorated. For example, thetemperature distribution of the solid-liquid interface portion 59 of thesingle crystal 15 and the vicinity thereof become nonuniform and,thereby, distortion occurs in the single crystal 15. When distortionoccurs in the single crystal 15, problems of, for example, cracking ofthe crystal occur during the cooling of the formed single crystal 15.

On the other hand, in the apparatus for producing a single crystal ofthe present embodiment, the ring-shaped members 47 are disposed on thecrucible 1 as described above. Consequently, the heating value of theside wall 1 a is increased at the portion provided with the lowerring-shaped member 47 and the portion provided with the upperring-shaped member 47, in addition to the lower end portion 1 d and theupper end portion 1 c of the side wall 1 a, compared with those at theother portions. Since the heating values of the portion provided withthe lower ring-shaped member 47 and the portion provided with the upperring-shaped member 47 are increased, the heating values of the portionsof the side wall 1 a other than the lower end portion 1 d, the portionprovided with the lower ring-shaped member 47, the portion provided withthe upper ring-shaped member 47, and the upper end portion 1 c areincreased compared with those in the known apparatus for producing asingle crystal. Therefore, the heating value distribution in the heightdirection of the side wall is uniformed compared with that in the knownapparatus for producing a single crystal.

In this manner, in the apparatus for producing a single crystal of thepresent embodiment, the temperature of the side wall 1 a is increased atthe portion provided with the lower ring-shaped member 47 and theportion provided with the upper ring-shaped member 47, in addition tothe lower end portion 1 d and the upper end portion 1 c of the side wall1 a, compared with those at the other portions. Since the temperaturesof the portion provided with the lower ring-shaped member 47 and theportion provided with the upper ring-shaped member 47 are increased, theheating values of the portions other than the lower end portion 1 d ofthe side wall 1 a, the portion provided with the lower ring-shapedmember 47, the portion provided with the upper ring-shaped member 47,and the upper end portion 1 c are also increased compared with those inthe known apparatus for producing a single crystal. Therefore, thetemperature distribution in the height direction of the side wall isuniformed compared with that in the known apparatus for producing asingle crystal. When the distributions of the heating value and thetemperature are thus uniformed in the height direction of the side wall1 a of the crucible 1, as shown in FIG. 12 and FIG. 13, a flow whichrises smoothly along the inner surface of the side wall 1 a of thecrucible 1 by the natural convection is formed in the melt 25 in thecrucible 1. Therefore, an undesirable complicated convection pattern isresistant to be exhibited in contrast to that in the known apparatus forproducing a single crystal.

In this manner, since the apparatus for producing a single crystal ofthe present embodiment is provided with ring-shaped members 47 inbetween the lower end portion 1 d and the upper end portion 1 c of theside wall 1 a, the lower ring-shaped member 47 and the upper ring-shapedmember 47 also generate heat in addition to the lower end portion 1 dand the upper end portion 1 c of the side wall 1 a by driving thehigh-frequency generation device 49, as described above, so that thetemperature distribution in the height direction of the side wall 1 a ofthe crucible 1 is uniformed. Consequently, the distribution of the heatgeneration in the height direction of the side wall 1 a of the crucible1 can be controlled, the convection of the melt 25 in the crucible 1 canbe controlled, and a flow which rises smoothly along the inner surfaceof the side wall 1 a of the crucible 1 by the natural convection can beformed in the melt 25 in the crucible 1, so that the melt 25 in thecrucible 1 is resistant to exhibit a previously known undesirableconvection pattern. Therefore, the solid-liquid interface portion of thesingle crystal can be flattened regardless of conditions, e.g., the sizeand the shape of the crucible, the occurrence of defects, cracks, andthe like can be reduced, and the fraction defective can be reduced inthe production of the single crystal.

Furthermore, since the solid-liquid interface portion of the singlecrystal can be flattened, the quality of the produced single crystal canbe improved. In addition, since the quality of the produced singlecrystal can be improved and the occurrence of cracks and the like of thecrystal can be suppressed, the productivity of the crystal can beimproved.

In the present embodiment, the ring-shaped members 47 are disposed intwo stages one above the other. However, the ring-shaped member 47 maybe disposed in a single stage, or the ring-shaped members 47 may bedisposed in at least three stages. The number of stages of thering-shaped members 47 to be disposed is appropriately determined inaccordance with, for example, the size of the crucible.

In the present embodiment, the ring-shaped members 47 disposed in thecircumferential direction of the outer surface of the side wall 1 a ofthe crucible 1 are used as the wall-side heating members. However, thewall-side heating member is not necessarily in the shape of a series ofring and may take various forms as long as the member is extended in thecircumferential direction of the outer surface of the side wall 1 a. Forexample, the wall-side heating member can also be composed of, forexample, pieces of the member intermittently connected into the shape ofa ring at appropriate spacings in the circumferential direction of theouter surface of the side wall 1 a of the crucible 1. In this case, thepieces of the member must be made into a shape long-extended in thecircumferential direction of the outer surface of the side wall 1 a ofthe crucible 1 compared with that in the height direction of the sidewall 1 a of the crucible 1, and furthermore, it is desirable that thesepieces of the member are disposed equidistantly in order to heatuniformly the side wall of the crucible 1.

Seventh Embodiment

The seventh embodiment of the apparatus of producing a single crystal,according to the present invention, will be described below withreference to FIG. 17 and FIG. 18. FIG. 17 is a sectional view showingthe schematic configuration and the operation of the apparatus forproducing a single crystal, according to the present invention, in astage of formation of a taper portion of a single crystal. FIG. 18 showsa comparison of temperature distributions of the bottoms of theapparatus for producing a single crystal, according to the presentinvention, and a known apparatus for producing a single crystal. In thepresent embodiment, the same elements and operations as those in thesixth embodiment are indicated by the same reference numerals as in thesixth embodiment, explanations thereof will not be provided, andconfigurations, characteristic portions, and the like different fromthose in the sixth embodiment will be described.

The apparatus for producing a single crystal of the present embodimentis different from that of the sixth embodiment in the point that abottom-side heating member for heating a central portion of the bottomof a crucible is disposed in addition to the ring-shaped members servingas wall-side heating member. As shown in FIG. 17, the apparatus forproducing a single crystal, according to the present embodiment, isprovided with a bottom-side heating member 65 composed of a heatconducting member 61 made of a cylindrical or disk-shaped memberdisposed at a central portion of the outer surface of the bottom 1 b ofthe crucible 1 and a disk-shaped heat generation portion 63 providedwith the heat conducting portion 61 at a central portion. The heatgeneration portion 63 is formed to have a diameter larger than thediameter of the heat conducting portion 61, and to have a diameter atleast two-thirds the diameter of the bottom 1 b of the crucible 1. Whenthe diameter of the heat generation portion 63 is thus made to be atleast two-thirds the diameter of the bottom 1 b of the crucible 1, theheat generation portion 63 tends to generate heat by high-frequencyelectromagnetic field and, therefore, the heating capacity of thebottom-side heating member 65 can be improved. The bottom-side heatingmember 65 disposed in the bottom 1 b side of the crucible 1 is containedin a refractory 9 together with the crucible 1.

The bottom-side heating member 65 composed of the heat conductingportion 61 and the heat generation portion 63 is formed from anelectrically conductive, high-melting point metallic material, e.g.,iridium, platinum, tungsten, or molybdenum, similarly to the crucible 1and the ring-shaped member 47. The bottom-side heating member 65 can beformed integrally with the crucible 1 while being connected with thebottom 1 b of the crucible 1, or be formed separately from the crucible1, followed by being attached to the bottom 1 b of the crucible 1.Furthermore, the heat conducting portion 61 and the heat generationportion 63 of the bottom-side heating member 65 can be formed separatelyfrom each other. When the bottom-side heating member 65 is formedseparately from the crucible 1, the bottom-side heating member 65 can beformed from the same material as the material for forming the crucible1, or be formed from a different material. When the bottom-side heatingmember 65 is formed separately from the crucible 1, it is desirable thatthe bottom-side heating member 65 is attached while the heat conductingportion 61 is in contact with the crucible 1 as strong as possible.

In the apparatus for producing a single crystal of the presentembodiment having such a configuration, an electromagnetic fieldgenerated by the high-frequency coil 11 concentrates particularly on acorner portion. Consequently, a periphery of the heat generation portion63 of the bottom-side heating member 65 also generates heat in additionto the periphery of the bottom 1 b of the crucible 1, i.e. the lower endportion 1 d of the crucible 1. The heat generated from the periphery ofthe heat generation portion 63 of the bottom-side heating member 65 isconducted from the heat generation portion 63 to the central portion ofthe bottom 1 b of the crucible 1 via the heat conducting portion 61 byheat conduction, and the central portion of the bottom 1 b of thecrucible 1 is heated. Therefore, in the distribution of the heatingvalue of the bottom 1 b per unit volume, a peak is observed at thecentral portion of the bottom 1 b of the crucible 1 in addition to atthe periphery of the bottom 1 b. As a result, in the temperaturedistribution of the bottom 1 b of the crucible 1, as is clear from thetemperature distribution 201 indicated by a solid line shown in FIG. 18,a peak is observed at the central portion of the bottom 1 b of thecrucible 1 in addition to at the periphery of the bottom 1 b.

On the other hand, with respect to a known apparatus for producing asingle crystal, provided with no bottom-side heating member 65, in thedistribution of the heating value of the bottom per unit volume, a peakis observed only at the periphery of the bottom of the crucible 1. As aresult, in the temperature distribution of the bottom of the crucible,as is clear from the temperature distribution 203 indicated by a brokenline shown in FIG. 18, a peak is observed only at the periphery of thebottom of the crucible. In the known apparatus for producing a singlecrystal, the central portion of the crucible is in a condition of beingat a lowest temperature. The temperature of the central portion of thebottom of the crucible becomes lower as the diameter of the bottom ofthe crucible is increased. Therefore, in the known apparatus forproducing a single crystal, a melt flow which rises from the centralportion of the bottom of the crucible may not be formed depending on theconditions, e.g., the size and the shape of the crucible, and thereby, amelt flow which spreads in the radius direction, from the solid-liquidinterface portion of the single crystal toward the inner surface of theside wall of the crucible, may not be formed. Consequently, the shape ofthe solid-liquid interface portion of the single crystal formedconnecting with the seed crystal is disturbed and becomes in an unevenstate, a crystal having poor quality may be produced, and cracks mayoccur in the crystal.

Previously, even when the temperature of the central portion of thebottom of the crucible is low and, thereby, a melt flow which spreads inthe radius direction, from the solid-liquid interface portion of thesingle crystal toward the inner surface of the side wall of thecrucible, is not formed, the crystal is rotated when a single crystal ispulled up, so that the melt flow which spreads in the radius direction,from the single crystal toward the inner surface of the side wall of thecrucible, can be formed. However, in the stage of forming a taperportion of the single crystal from the seed crystal, even when thecrystal is rotated, since the diameters of the seed crystal and thetaper portion of the single crystal are small, the centrifugal forcegenerated by the rotation of the crystal is also small, so that a meltflow which spreads in the radius direction is weaker than that in thestage after the formation of the straight body portion of the singlecrystal is started. Therefore, it is difficult to flatten thesolid-liquid interface portion of the single crystal only by therotation of the crystal. Such a situation also occurs when only thewall-side heating member is disposed on the crucible as in the apparatusfor producing a single crystal of the first embodiment.

On the other hand, in the apparatus for producing a single crystal ofthe present embodiment, as shown in FIG. 17, since the bottom-sideheating member 65 is disposed on the crucible 1, the heating value atthe central portion of the bottom 1 b of the crucible 1, as well as theperiphery of the bottom 1 b. becomes higher than those of the otherportions. Since the heating value at the central portion of the bottom 1b is increased, the temperature of the central portion of the bottom 1 bof the crucible 1, as well as the periphery of the bottom 1 b, becomeshigher than those of the other portions. When the temperature of thecentral portion of the bottom 1 b is increased as described above, aflow of the melt 25 is formed, while the flow rises in the vicinity ofthe center axis of the crucible 1 from the central portion of the bottom1 b along this center axis to reach the vicinity of the solid-liquidinterface portion 59 of the seed crystal 13 and the single crystal 15,and spreads in the radius direction, from the vicinity of thesolid-liquid interface portion 59 of the seed crystal 13 and the singlecrystal 15 toward the inner surface of the side wall 1 a of the crucible1.

In this manner, since the apparatus for producing a single crystal ofthe present embodiment is provided with the bottom-side heating member65 for heating the central portion of the bottom 1 b of the crucible 1,the central portion is also heated in addition to the periphery of thebottom 1 b of the crucible 1 by driving the high-frequency generationdevice 49, as described above. Consequently, the flow of the melt 25 isformed, while the flow rises from the central portion of the bottom 1 bof the crucible 1 to reach-the vicinity of the solid-liquid interfaceportion 59 of the seed crystal 13 and the single crystal 15, and spreadsin the radius direction, from the vicinity of the solid-liquid interfaceportion 59 of the seed crystal 13 and the single crystal 15 toward theinner surface of the side wall 1 a of the crucible 1. Therefore, thesolid-liquid interface portion of the single crystal can be flattenedregardless of conditions, such as the size and the shape of thecrucible, the occurrence of defects, cracks, and the like can bereduced, and the fraction defective can be reduced in the production ofthe single crystal.

In the present embodiment, the ring-shaped members 47 serving aswall-side heating members are disposed. However, when any wall-sideheating member is unnecessary depending on the conditions, e.g., thesize and the shape of the crucible, the ring-shaped member 47 serving asa wall-side heating member may not be disposed in the configuration.

In the present embodiment, the bottom-side heating member 65 composed ofthe heat conducting member 61 made of the cylindrical or disk-shapedmember and the disk-shaped heat generation portion 63 is included.However, the bottom-side heating member can have various configurationsin which the heat is generated by the high-frequency generation device49, and the central portion of the bottom 1 b of the crucible 1 can beheated.

For example, as shown in FIG. 19, a disk-shaped member made ofelectrically conductive, high-melting point metallic material isdisposed on the bottom surface in a refractory 9 so as to serve as aheat generation portion 67, and a heat insulating member 71 having athrough hole 69 in the central portion and having a diameter equal tothe inner diameter of the refractory 9 is superposed on this heatgeneration portion 67. A crucible 1 is disposed on the heat insulatingmember 71 while the central portion of the bottom 1 b of the crucible 1is aligned with the through hole 69 of the heat insulating member 71.With respect to the above-described bottom-side heating member 73, theheat generated from the periphery of the heat generation portion 67 isconcentrated on the central portion of the heat generation portion 67 byheat conduction, and the central portion of the bottom 1 b of thecrucible 1 is heated via the through hole 69 by radiation. In thismanner, the bottom-side heating member can also be composed of the heatinsulating member 71 constituting the heat conducting portion and theheat generation portion 67 which is a disk-shaped member, as in thebottom-side heating member 73. When the bottom-side heating member has aconfiguration as in the bottom-side heating member 73, the number ofcomponents can be reduced.

The bottom-side heating member can also have a configuration in which,for example, a heat generation portion is formed from an electricallyconductive, high-melting point metallic material into the shape of acircular ring, a cylindrical heat conducting portion formed from anelectrically conductive, high-melting point metallic material isdisposed coaxially with this heat generation portion, and a rod-shapedconnection member formed from a high-melting point metallic material isdisposed in the shape of a spoke between the heat generation portion andthe heat conducting portion. In bottom-side heating members havingvarious configurations, the heat conducting portion is not necessarilyin the shape of a disk or a cylinder, and can be made into the shape ofa prism or the like.

In the sixth and seventh embodiments, the ring-shaped members 47 servingas wall-side heating members and the bottom-side heating member 65 arein the state of being fixed to the crucible 1. The wall-side heatingmember and the bottom-side heating member may be configured to beattachable and detachable at will, and be detached from the cruciblewhen unnecessary, for example. Furthermore, a mechanism which allows thewall-side heating member and the bottom-side heating member to beattached to and detached from the crucible can also be disposed. Forexample, as shown in FIG. 20, a heat insulating member 77 having athrough hole 75 in a central portion and having a diameter equal to theinner diameter of a refractory 9 is disposed above a bottom 9 c in therefractory 9. A bottom-side heating member 65 which has the sameconfiguration as in the seventh embodiment and which is formedseparately from the crucible 1 is disposed between the bottom 9 c in therefractory 9 and the heat insulating member 77. Here, connection members79 disposed penetrating the bottom of the refractory 9 are connected tothe lower surface of the heat generation portion 63 of the bottom-sideheating member 65. The connection members 79 are connected to a drivingmechanism 81, e.g., an oil hydraulic or air jack, a motor andrack-and-pinion type driving mechanism, or the like, for verticallytransporting the bottom-side heating member 65, and the connectionmembers 79 and the driving mechanism 81 constitute a heating membertransporting device 83.

By adopting such a configuration provided with the heating membertransporting device 83, a heat conducting portion 61 of the bottom-sideheating member 65 can be detached from the bottom 1 b of the crucible 1,if necessary, and therefore, the heating of the central portion of thebottom 1 b can be stopped. In the stage of, for example, forming a taperportion 15 a of a single crystal 15 from a seed crystal 13, thebottom-side heating member 65 is pushed up by the heating membertransporting device 83 so as to bring the heat conducting portion 61 ofthe bottom-side heating member 65 into contact with the bottom 1 b ofthe crucible 1, and when the diameter of the taper portion 15 a of theseed crystal 15 becomes adequately increased, the bottom-side heatingmember 65 is moved downwards so as to prevent the heat of thebottom-side heating member 65 from being conducted to the centralportion of the bottom 1 b of the crucible 1. The configuration providedwith such a heating member transporting device can also be applied tothe wall-side heating member. By adopting the above-describedconfiguration, the solid-liquid interface portion 59 of the seed crystal15 can be controlled at an optimum state and, therefore, a singlecrystal having higher quality can be produced.

The technologies of producing a single crystal shown in the first to theseventh embodiments can be used appropriately in combinations.

The present invention is not limited to the production apparatuseshaving the configurations of the first to the seventh embodiments, butcan be applied to apparatuses for producing a single crystal, theapparatus having various configurations in which crucibles are subjectedto the high-frequency heating. Furthermore, apparatuses for producing asingle crystal, according to the present invention, are particularlyeffective for forming a single crystal of oxide, e.g., gadolinium,gallium, garnet, cerium-activated gadolinium silicate, or the like, andin addition, can be used for producing other various types of singlecrystal.

1. A method for producing a single crystal comprising the step ofheating a crucible which holds a raw material and pulling up a seedcrystal while the seed crystal is in contact with a melt of the rawmaterial so as to produce a single crystal, wherein the crucible isheated by a high-frequency induction heater including a high-frequencycoil for heating the crucible, and wherein the diameter of the singlecrystal is increased during formation of a taper portion of the singlecrystal in an initial stage of growth of the single crystal, and thesingle crystal is cylindrically grown connecting with the taper portionduring formation of a straight body portion of the single crystal, whilethe radiation heat which reaches the taper portion of the single crystalfrom an inner surface of said crucible is blocked during the formationof the taper portion of the single crystal.
 2. A method for producing asingle crystal comprising the step of heating a portion in the sidelower than the upper end portion of a crucible which holds a rawmaterial of a single crystal and pulling up a seed crystal while theseed crystal is in contact with a melt of the raw material so as toproduce a single crystal, wherein the crucible is heated by ahigh-frequency induction heater including a high-frequency coil forheating the crucible, and wherein the diameter of the single crystal isincreased during formation of a taper portion of the single crystal inan initial stage of growth of the single crystal, and the single crystalis cylindrically grown connecting with the taper portion duringformation of a straight body portion of the single crystal, while theradiation heat toward an upper portion above the upper end portion ofsaid crucible is blocked during the formation of the straight bodyportion of the single crystal.
 3. An apparatus for producing a singlecrystal comprising a crucible for holding a raw material, ahigh-frequency generation device including a high-frequency coildisposed surrounding said crucible, and a crystal transporting devicefor rotating and transporting a seed crystal upwards from the inside ofsaid crucible, wherein the apparatus comprises a wall-side heatingmember for heating a portion in between the upper end portion and thelower end portion of the side wall of said crucible by the operation ofsaid high-frequency generation device.
 4. The apparatus for producing asingle crystal, according to claim 3, wherein said wall-side heatingmember comprises a protrusion-shaped member which is made of anelectrically conductive material and which is disposed in between theupper end portion and the lower end portion of the outer surface of theside wall of said crucible while being extended along thecircumferential direction of the outer surface of the side wall of saidcrucible.
 5. An apparatus for producing a single crystal comprising acrucible for holding a raw material, a high-frequency generation deviceincluding a high-frequency coil disposed surrounding said crucible, anda crystal transporting device for rotating and transporting a seedcrystal upwards from the inside of said crucible, wherein the apparatuscomprises a bottom-side heating member for heating a central portion ofthe bottom by the operation of said high-frequency generation device, onthe bottom of said crucible.
 6. The apparatus for producing a singlecrystal, according to claim 5, wherein said bottom-side heating membercomprises a heat conducting portion made of a heat conductive materialfor conducting heat to a central portion of the outer surface of thebottom of said crucible and a board-shaped heat generation portion whichhas a diameter larger than the diameter of the heat conducting portionand which is made of an electrically conductive material.
 7. Theapparatus for producing a single crystal, according to claim 5, whereinsaid bottom-side heating member comprises a heat insulating member madeof a heat insulating material having a through hole at the position inaccordance with a central portion of the outer surface of the bottom ofsaid crucible and a board-shaped heat generation portion which has adiameter larger than the diameter of the through hole of said heatinsulating member and which is made of an electrically conductivematerial.
 8. An apparatus for producing a single crystal comprising acrucible for holding a raw material, a heating device for heating theraw material in said crucible, and a crystal transporting device fortransporting a seed crystal upwards from the inside of said crucible,wherein the heating device is a high-frequency induction heaterincluding a high-frequency coil for heating the crucible, and whereinthe apparatus further comprises a heat conducting member which extendsupwards at least from the vicinity of the upper end portion of the sidewall of said crucible, which surrounds a formed single crystal, andwhich is made of a material having heat conductivity.
 9. An apparatusfor producing a single crystal comprising a crucible for holding a rawmaterial, a heating device for heating the raw material in saidcrucible, and a crystal transporting device for transporting a seedcrystal upwards from the inside of said crucible, wherein the heatingdevice is a high-frequency induction heater including a high-frequencycoil for heating the crucible, and wherein the apparatus furthercomprises an interface portion radiation heat blocking member forblocking, at least during cooling after the formation of a singlecrystal, the radiation heat toward an upper portion above the interfaceportion between a taper portion, which is connected with a seed crystalof the formed single crystal and has a diameter gradually becomingincreased, and a cylindrical straight body portion, which is connectedwith the taper portion of the formed single crystal.
 10. The apparatusfor producing a single crystal, according to claim 9, wherein theapparatus further comprises a heat conducting member which extendsupward at least from the vicinity of the upper end portion of the sidewall of said crucible, which surrounds a formed single crystal, andwhich is made of a material having heat conductivity.
 11. The apparatusfor producing a single crystal, according to claim 10, wherein theradiation heat blocking member is located at the upper end of the heatconducting member.
 12. The apparatus for producing a single crystal,according to claim 9, further comprising a refractory member surroundingthe crucible and extending above the crucible, and wherein the interfaceportion radiation heat blocking member is a lid portion of therefractory member.
 13. An apparatus for producing a single crystalcomprising a crucible for holding a raw material, a heating device forheating the raw material in said crucible, and a crystal transportingdevice for transporting a seed crystal upwards from the inside of saidcrucible, wherein the heating device is a high-frequency inductionheater including a high-frequency coil for heating the crucible, andwherein the apparatus comprises an in-crucible radiation heat blockingmember which surrounds a single crystal and which blocks the radiationheat from an inner surface of said crucible toward the single crystalpositioned in the inside of said crucible and an in-crucible radiationheat blocking member transporting device for transporting saidin-crucible radiation heat blocking member in a vertical direction,while said in-crucible radiation heat blocking member transportingdevice transports said in-crucible radiation heat blocking member to theposition surrounding a taper portion of the single crystal duringformation of the taper portion of the single crystal to increase thediameter of the single crystal in an initial stage of growth of thesingle crystal and transports said in-crucible radiation heat blockingmember to the position at a distance from the single crystal duringformation of a straight body portion of the single crystal cylindricallygrown connecting with the taper portion.
 14. The apparatus for producinga single crystal, according to claim 13, wherein the in-crucibleradiation heat blocking member is a radiation heat shielding plate in ashape of a cone along the taper portion of the single crystal.
 15. Theapparatus for producing a single crystal, according to claim 14, whereinan angle of inclination of the conical surface of the radiation heatshielding plate is substantially equal to the angle of inclination ofthe taper surface of the taper portion of the single crystal.
 16. Anapparatus for producing a single crystal comprising a crucible forholding a raw material, a heating device for heating the raw material insaid crucible, and a crystal transporting device for transporting a seedcrystal upwards from the inside of said crucible, wherein the heatingdevice is a high-frequency induction heater including a high-frequencycoil for heating the crucible, and wherein the apparatus comprises astraight body portion radiation heat blocking member which can passthrough a single crystal and which blocks the radiation heat toward anupper portion above the upper end portion of said crucible and astraight body portion radiation heat blocking member transporting devicefor transporting said straight body portion radiation heat blockingmember in a vertical direction, while the heating device heats a portionin the side lower than the upper end portion of said crucible, and saidstraight body portion radiation heat blocking member transporting devicetransports said straight body portion radiation heat blocking member tothe position at a distance from the upper end portion of said crucibleduring formation of a taper portion of the single crystal to increasethe diameter of the single crystal in an initial stage of growth of thesingle crystal and positions said straight body portion radiation heatblocking member in between the outer perimeter surface of the straightbody portion of the single crystal and the inner perimeter surface ofsaid, crucible or in between the outer perimeter surface of the straightbody portion of the single crystal and the upper end portion of saidcrucible during formation of the straight body portion of the singlecrystal cylindrically grown connecting with the taper portion.